# HELP Check Engine Light Flashing



## mkwl

:realmad:On my way up to school, driving at around 70+/-MPH for about 2.5 hrs, my check engine light started flashing about every 15-20 minutes (would flash for 3-18 flashes each time) then go off. GM manual says this is a misfire detected in the engine- any thoughts? Is it going to be a problem to drive the truck as is until I can get it looked at (middle of next week)? The truck had flashed like this in the past, but never so much all in one trip. It seems to only do it when I'm driving on the highway.

I'm thinking it may be the need for new wires/plugs. I'm going to have a GMC dealer install them- any idea what I'm looking at cost wise?

Not sure if it matters, but I recently put in a K&N drop in air filter.

Thanks,
Matt


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## terrapro

The filter shouldn't have done anything bad unless you knocked you mass air flow sensor out in the process. Check your spark related parts like plugs, wires, modules, and sensors you can readily reach.

Do a quick visual check through the engine compartment first to make sure everything is hooked up. You might have knocked something loose.


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## mkwl

Is there any good way to check the wire/plug condition?

How hard is it to replace the plugs and wires? Proper procedure?

How much for the GM parts?


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## brad96z28

ck the code but. But sometimes the oil from the k&n gets on the maf and causes issues. But get it scanned could be a thousand things.Then go from there. Otherwise a never ending guessing game


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## Milwaukee

How many miles on this engine?

It time for tune up.


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## mkwl

About 72,000 miles on the truck.

Is running the truck with the light occasionally flashing (usually only on the highway) going to damage anything until I can get it looked at?


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## mcginner

When the engine light is flashing it means you are doing harm to the catalictic convertors which are very expense for those truck and have a chance of plugging up and cause your truck to run like a bag of crap.
Get the truck check by a pro to see why the light is on. You most likily do need new plug & wire set, a fuel filter would be a good idea too.
Also the oil from the K&N filter can cause problems with the MAF sensor. Clean the sensor with brake cleaner.


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## stillen

mine would flash, it was a p0304 code, cylinder four was misfiring..... The flashing means unburnt fuel was headed down towards the cat,,,,, thats bad...... butmy truck had 270k on it. it was a 2001, 5.3.... ran like a champ, i traded it for my dodge...


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## Sydenstricker Landscaping

Mine did that too, flashed occasionally and go off. It turned out to be a bad O2 sensor. But keep an eye on the MAF, those oiled air filters suck. Get some good MAF cleaner by CRC and clean it up good. Possibly invest in a nice dry flow filter in place of the K&N. Much better for your engine. A tune up is easy to do, shouldnt take more than 20 minutes in your drive with very, very basic hand tools ( ratchet, plug gap gauge, extension and 5/8 deep well socket.) The plugs are kind of pricey but it will run much better after that. Dont pay a bunch of money to a dealer to tune that thing up. Should cost under $100 to do it yourself. And it is not like you could cross any wires, lol. But get the code scanned instead of the guessing game.


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## 2COR517

mcginner;801393 said:


> When the engine light is flashing it means you are doing harm to the catalictic convertors which are very expense for those truck and have a chance of plugging up and cause your truck to run like a bag of crap.
> Get the truck check by a pro to see why the light is on. You most likily do need new plug & wire set, a fuel filter would be a good idea too.
> Also the oil from the K&N filter can cause problems with the MAF sensor. Clean the sensor with brake cleaner.


NO! NO! NO!

Only use Mass Airflow Cleaner on your MAF. You can get it at Autozone, CRC produces it. When you clean the MAF, use only the spray, and do not touch the wires with anything. No compressed air, Q-tips, the spray nozzle, nothing.

If you have an oiled K&N filter upstream of your MAF, get rid of it. If it hasn't already, it will cost you a new MAF. They shouldn't even sell those things. Get a nice paper filter. WIX or NAPA Gold. All those K&N do is let more dirt in your engine, and lighten your wallet. The stock paper filter is more than capable of flowing enough air at WOT.

Sounds like a full tuneup is in order. Pull the Throttle body and clean it. Put some SeaFoam through the intake. New AC Declo plugs. For wires, ACD or Napa premium.

Don't forget your fuel filter and PCV Valve. And at your mileage O2 sensors may be in order. They can slowly go bad, without throwing a code.


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## brad96z28

lol never seen iridium plugs go bad by 70k
This thread will go on for ever til we get a code!


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## nightandday

I believe if this is a 6.0 366ci. gas job you will find that a coilpack has gone bad. find out which cylinder is throwing the code. Also did you power wash the engine or degrease it recently? I did both to my 01 2500hd and burn out a coil pac. truck ran fine at first but in a matter of two driving hours it-would no longer idle correctly. A wet air filter (one containing spray oil is not the wisest choice in my opinion it has the ability to pick up to much fine particles if it is oiled by you upon your purchase. the k&n is pre oiled and in the consumer reports it falls near the worst filter, due to the fact that it impedes air flow rather than promote it . hope that helps


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## Cosmic Charlie

Bad coil pack according to my ASE mechanic, mine was failing at hiway speeds but ok around town. I woiuld reset the check engine light and drive ONLY around town for 2 weeks and it would pass inspection, but later on the hiway the flashing light would come on, and stay constant later - until I repeat the procedure for next years sticker, 3 years of stickers and counting !

ps I usually don't drive this truck on the hiway ... just plowing and boat launching, I would have it fixed if you drive on the hiway regularly, I don't

again I don't usually drive on the hiway and my coil pack is fine at under 40 MPH (+-)


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## mkwl

Okay- any idea how much a coil pack is (installed)? I'm going to try and get it scanned on Tuesday- will know better then what it will need.


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## nightandday

I would guess it is going to be around $75 USD but You may need more than one


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## mkwl

Okay- not too bad- I assume the coil pack is easily accessible (the unit the wire connects to off the plug)?


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## nightandday

That is correct. It is a realy easy fix to do yourself also if you find out which pac went bad they should be able to tell you that much and what the location of it is. I know the dealers in my town are $90 / Hr


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## mkwl

Okay, now, when I get it scanned- how will I know if it's the pack that's gone bad, versus the plug, versus the wire.....?


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## Newdude

mkwl;801968 said:


> Okay, now, when I get it scanned- how will I know if it's the pack that's gone bad, versus the plug, versus the wire.....?


If you have 2 cylinders misfiring and they run on the same coil pack, I would think you'd have to check for spark. If there isnt any, that could tell you if power is leaving the coil for that cylinder or not. If the coil is fine, you ccan check the resistance in the plug wires.


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## mkwl

Okay- going to get it scanned (hopefully) after class today. the thing that puzzles me (and a mechanic friend of mine) is why it only seems to do it at highway speeds (60-72 MPH), and it's very sporatic- sometimes 30 flashes, sometimes just 3.

Does this sound like a coil? It runs fine, if the light wasn't flashing, I wouldn't even know there was a problem.


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## Cosmic Charlie

Same Here

I'm not 100 % sure it's the coil pack

Now maybe you can tell me ?

Mine runs 100 % with or without the check engine light on - go figure

I do run Techron through the fuel system each year with no change


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## mkwl

Okay- took my truck advance auto- borrowed their OBDII scanner and found: Code P0300- Random/Multiple Cylinder Misfire. Any thoughts? Does this mean that it's a random misfire, more than one cylinder is misfiring, or both? The guy at advance said there's really no way to tell whether or not it's the coil, wire, etc, just start replacing parts and hope for the best!?!?

The truck runs 100% fine (knock on wood so far)- light flashes randomly on the highway- I'm at a loss???


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## Newdude

mkwl;802194 said:


> The guy at advance said there's really no way to tell whether or not it's the coil, wire, etc, just start replacing parts and hope for the best!?!?


Sounds like he wanted your money haha.

http://autorepair.about.com/od/troubleshooting/ss/coiltest-manual.htm

http://www.aa1car.com/library/dis.htm


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## mkwl

Well, I changed the wires and plugs- problem is still there. So, off to the dealer the truck went today :crying::realmad:- hopefully they'll get it into the shop tomorrow and have some idea what the problem is.


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## Luke_P

gotta love some parts guys(or mechanics for that matter) don't trouble shoot throw parts at it!! not saying it will work for you because your trucks running well when the code trips this works better when the vehicle has a noticable miss. but if you can get a ir gun(thermometer that looks like a pistol) next time its flashing stop quick and shoot all the manifolds and each side of the y pipe if you can find a reasonable temperature drop on a couple cylinders or one sid eof the y you've either narrowed it down or found the weak ones. (the incomplete combustion caused by the misfires can result in a colder exhaust temp)


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## mkwl

Well, it's at the dealer now, so hopefully they'll have a diagnosis to me by tomorrow and I'll know about how much $$$ I have to shell out to get yet another problem fixed :crying:


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## SawHoss

I have the exact same problem with my truck. Around town, and anything under 65-70, the truck runs perfect. Its once I get above 70 that the truck begins to flash the check engine light, especially when the truck is coasting down a hill. At first I thought it was my transmission slipping out of overdrive, but then advance flashed it, and it said random/multiple cylinder misfire. I then had my mechanic look at it, and he cleaner off the MAF sensor because it was gummed up with the oil from the k&n filter (go figure) so I swapper out that for a Fram, and it ran fine for a while, but it is still acting up. My mechanic said it may be a bad intake gasket, so that is next. But if you find out for sure that it is a bad coil pack, then that is next on my list. Truck has 128000 and had new plugs and wires done about 2 years ago.


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## mkwl

Well, got a call from GM today- they wanted to start throwing parts at it hoping to solve the problem- I wasn't going to go for a $1,000+ repair bill so I cut my losses at $160 diagnostic fee (all they could tell me was that it was misfiring- DUH- and cylinder 1 was the worst). So, I have my truck back now- same problem- looking for possibilities.....:crying:

I'm honestly getting pretty fed up with GM- I called GM HQ to complain (truck has 71,000 miles on it and the DEALER can't even figure out what's wrong!), they basically said at 71,000 the truck is PAST it's optimal lifespan, and I'm probably due for a NEW GM TRUCK!!!:realmad: IDK what I'm going to do, but I don't think I'll be going with GM in the future if they keep this BS up!


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## Newdude

Do you know of any other GM dealers in your area? Maybe a good independent shop?


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## Luke_P

seriously man ditch the dealer. Generally speaking (and this is only my opinion so i apoligize to any dealer mechanics who beat the odds) dealers are usually the bottom of the totem pole for trouble shooting, especially when the scanner comes up zip. they work on mainly NEW VEHICLES they do not get a lot of trouble shooting jobs and are usually a little out of practice. I am not trying to bragg but I have fixed many vehicles assorted local dealers just couldn't figure out. and for good reason I can spend 12 hours chasing a small problem and say hey give me $200 a dealer isn't going to say well we are $100 an hour 12 hours how about $300. They would rather spend your money on parts or someone else's money changing brakes or a intake gasket and tell you sorry can't find it. go to a good independant you know the guy that is always booked for a week, there's a reason. Or get your mechinc buddy more involved the dealer is going to try the same things they are and charge you 30-50% more

heres a couple new ideas

switch the coil pack from Cyl 1 to say 7 or whatever see if the miss moves with it, Know anyone else with a similar truck borrow one of theirs(coil) see if itgoes away (the miss). Most guys on the front desk will never admit it but scanners are not all seeing gods some times you just gotta try stuff and see what happens. get B&B on here and pick his brain the guy is a GM machine I do not profess to be a mechanic but I am not bad, 

B&B is a mechanic and from what you can learn about a person on a forum a damned professional one. and I have never seen him post a "it might work this way or might be that" he tells you exactly what to try and how to go about it. 

With some time and knowledgable help I am sure you can figure this out


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## Luke_P

ps I was kinda stuck on ignition symptoms but the following can also cause lean running conditions which will set that code

1 stuck egr (open) 
2 vacum leaks in intake
3 air entering intake ducting unmetered (ie a split in your air ducting behind your MAF sensor)
4 fuel injectors
5 o2 sensor(s)

how to check

1. I do not have reliable recent experience on that egr and my manuals escape me right know, if it is vacum acuated you can watch it see if it moves or looks stuck in one position or not. if it is electric have a good shop or your buddy check it out you can usually do some checks on them with a good scanner before just throwing one on. I believe yours is electric. You can remove either type and see if the pintle is clean\pitted that can sometimes be the case.

2. listen and look, check all vacum lines that leave the intake, I have seen a vacum line which went to the transmission develop a leak halfway in between and wreak havoc. I have done the following and seen it done, some may dissapprove open a propane torch slightly (unlit) and wave around the intake(the intake manifold not your air intake) or any suspected leaks if the motors rpm raises you have a intake leak as the propane is being sucked in and richening the mixture(providing more fuel)

3. LOOK LOOK LOOK I have seen this one personally on a couple trucks with aftermarket filters\intake piping and factory units as well. Could be a split in the piping (even reasonably small) loose hose clamp, cracked fitting, you are looking for problems behind the MAF sensor issues ahead of it can result in unfiltered air(still bad). But not the problem you are seeing.

4 anyone feel free to add\correct but injectors don't typically do random they usaully work well or they don't and are harder to trouble shoot with out digging deeper and having specialty tooling.

5 02 sensor try the rest first then consider 02's my off hand knowledge is a little weak but i believe your truck has a few (4?) two upstream of the cat and two down o2's can be little buggers they can test alright and still be bad, if there was only one I would say replace it anyways but 4 can add up$$$

options 1,2,3 are going to be the most likely sources of trouble that you could find on your own without much for tools\diagnostics


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## Luke_P

on edit by if the egr is clean\pitted i mean if its overly dirty clean it if its pitted replace it

good luck!!


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## B&B

Luke made some very accurate and unfortunately very correct comments about today's technicians..which many are not; they're simply parts replacer's now days. And much of that is simply due to the lack of incentive to put forth effort in their work and schooling since many dealerships fail to pay real techs for all their knowledge and qualifications. Their feeling is that why should they when they can hire said parts replacer's off the streets for less pay and sell more parts. So like anything else it's the bottom dollar driven scenario. If they can do it cheaper while selling parts along the way that may or may not be needed it's then a win win situation for them. But unfortunately it's also at the cost and satisfaction of the customer. And anyone whom has been in this business for any length of time will tell you that this is certainly nothing new or limited only to a GM dealership as it is, and has been happening for years across most of the major auto manufactures, many imports included. It's usually faster and more profitable to just throw parts at it than it is to actually pay a top notch "real" tech a fair hourly rate and investing many dollars into their schooling and qualifications to get them there to do proper diagnostics. Sure there's still many top shelf tech's at the dealerships around the country but they're also quickly finding that that just may not be in their best interests either. Dealerships are well known to make many promises at hire time but it doesn't take long these days for an intelligent employee to discover that they don't always deliver.

It's the same reason you'll find many tech now leaving the dealerships and migrating toward the smaller independent shops for a couple reasons. They reward better overall and care more not only for their techs but for the customers best interests also. Since without honest and quality work (something tough to find in parts replacer's and bottom dollar corporates) there's few repeat customers...which are so important to the smaller shops and they're well aware of that. 

In a nut shell Matt they basically could have fixed your truck, as they certainly had all the tools at their disposal to do so, they either just didn't have the knowledge or care on how to utilize them. So they either didn't want to put the proper diagnosis time into it or more likely he didn't know how to do it, rather they'd just throw parts on it or shove it out the door and move onto something easier and with faster profits and thus you were left the only option they offered you, which was that you pay until it's fixed. A shiny plaque on the wall, a spiffy clean uniform and a $100K worth of shiny new tools doesn't make a good tech. It takes knowledge and experience and the desire to further your education and just as importantly care...and so few do today for above said reasons.

A good shop with a good scanner can correctly diagnose your truck. An hours time with a fuel pressure gauge and a scanner in the hands of someone who knows how to fully utilize them; and more importantly comprehend the data they retrieve with them would have little time or effort into diagnosing it.

Luke mentioned that a scanner isn't an "instant tell all" (like many believe) and he's correct, they're not. But what they will do in the hands of a knowledgeable tech is lead him toward the correct road to rule out as many possible issues without just throwing part on it while checking critical data along the way. 

If the truck was in my shop the first thing I would do is get the scanner and fuel pressure gauge on it, checkfreeze frame data and then get it on the highway to monitor fuel pressure, long term fuel trims, 02 sensor voltages, injector pulse widths, 02 sensor cross counts as well as MAF activity...and of course fuel pressure. Armed with this data it would be a simple pinpoint the root issue.


Based on what you've done so far and knowing these trucks it's a realistically safe assumption on my part that you either have a leaking intake gasket, a restricted injector, or a MAF sending error-ed data info back to the ECM..possibly due to the MAF itself failing or an air leak between the MAF and the throttle body. And I can tell you without a shadow of a doubt that you DO NOT have an secondary ignition problem so don't waste your time swapping coils around. Instead, spend the time checking around and asking the locals where the best independent repair shop is. Often times their easy to spot without assistance as they will be the most busy one in town with a lot stuffed full of repair work.


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## mkwl

Thanks B&B- I'll take a look at the MAF, maybe try some MAF cleaner- that is the correct procedure for "cleaning" it?

What's the best way to identify a gasket leak?

I'll keep my eyes peeled for a good local garage...


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## Luke_P

B&B thanks for the input, I was just trying to put some ideas up for him to check out before he gave up\ sent it in you never know. My problem is I fix enough vehicles to be realitevly proficient but not enough to know trends or "known issues" on specific vehicles. And truth be told I am a weaker then I would like using live scan tools as the chance to use them only comes up for me every know and again. Again I was not trying to paint only GM guys with one brush. My personal experience with less then satisfactory service work comes from all of the big three, and a couple imports as well as independants. Nor was I pushing my methods as the "correct" way more so things he could try himself easily as no one else was putting much out there. I agree that a live scanner and a experienced guy willing to use it(along with tradiotional tools) and invest some time is worth its weight in gold. I am lucky as because I know a lot of mechanics(some dealer guys too!!) I can usually get one (a live scanner) and some knowledge thats not charged per hour.


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## Cosmic Charlie

ANOTHER CLUE ?

when my 2004 HD 2500 is cold, I have a intake or exhaust noise (leak ?) that goes away when warmed up. I've heard stories about the intake manifold bolts being under torqued at the factory so not to damage the plastic intake housing ? any truth ?

is it related to highway speed flashing check engine light ?


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## SawHoss

I have recently talked to my mechanic telling him about my own experiences along with others on plow site. The little difference that I have is that my intake manifold was warped about 5-6 years ago, and replaced by the previos owner (my dad) and he told me that the replacement manifold is much stiffer and resistant to warping compared to the original. With this being said, his advice to me to try on my own truck was to borrow a MAF sensor from a buddy with basically the same identical truck. Now I have not yet been able to borrow a sensor, but I should have results by the end of the weekend. (Borrow from someone who doesnt have the same problem) Thats about all the input that I can contribute to the conversation. Keep posting ideas/updates!


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## B&B

mkwl;803383 said:


> Thanks B&B- I'll take a look at the MAF, maybe try some MAF cleaner- that is the correct procedure for "cleaning" it?


Correct Matt. Get yourself some MAF cleaner and pop the MAF off the truck and give it a good thorough internal cleaning adhering to some of the tips that 2COR mentioned in his previous post. It's also a good periodic maintenance procedure to do about every 20K miles or so on ANY MAF equipped vehicle since just like anything else in service, it's fine strand internal sensor wires get contaminated with debris during use. Mostly from paper fibers from the air filter if you run a paper one, or worse yet stray oil from an over oiled oil/gauze aftermarket air filter.



mkwl;803383 said:


> What's the best way to identify a gasket leak?


The old standby test (I'm sure Luke's familiar with this one) is to use carb cleaner and spray around the edges of the intake at the intake to cylinder head connection where the gaskets are. The problem on your truck and on any LS based engine is that the test isn't concluding due to the fact that on those engines one half of the sealing surface you can not access due to the design of the intake itself. If the leak is on the outboard side (valve cover side) it will show up but in most cases the air leak is actually on the underside facing the lifter valley; making the test inaccurate for diagnosis. The real method to determine an intake leak is to rule out other possibilities first using other diagnostic test. Like for example checking data of specific sensors with a scanner (like I mentioned in the previous post) and using that data to rule out any questionable possibilities. A good example: You would first check running fuel pressure. If it's within spec you would move on to monitoring the 02 sensors activity comparing one side to the other. If both are out of range by about the same amount then you'd know it's not an 02 issue since they seldom fail as a pair, so it's something affecting fueling and thus 02 reading upstream from there. Then you basically work upstream now knowing that both 02's are being affected so it has to be an issue that's affecting both banks of the engine (which would also rule out an injector issue in 99% of the cases), and only certain components or issues can affect both banks, such as an upstream air leak or a faulty/dirty MAF sending incorrect data. So you then move to the MAF streaming data to see if it's within spec, if it is then it can be narrowed down to an air leak somewhere between it and the cylinder heads which would be affecting the fueling (and hence the original 02's specs first checked). Once it's narrowed down we can then finalize it's very likely an intake gasket leak since they're a very very common issue to the LS engines anyway.

This is condensed version of the actual procedure and I'm sure it appears like a lengthy diagnosis but it's not. This can all be done in less than an hour including checking fuel pressure initially.

The difference between this method instead of just throwing parts on it is that this "process of elimination" so to speak is done with diagnostics, data, and previous knowledge.....not by throwing parts at it until it's fixed while lightening the owners wallet in the process.


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## B&B

Luke_P;803429 said:


> B&B thanks for the input, I was just trying to put some ideas up for him to check out before he gave up\ sent it in you never know. My problem is I fix enough vehicles to be realitevly proficient but not enough to know trends or "known issues" on specific vehicles. And truth be told I am a weaker then I would like using live scan tools as the chance to use them only comes up for me every know and again. Again I was not trying to paint only GM guys with one brush. My personal experience with less then satisfactory service work comes from all of the big three, and a couple imports as well as independants. Nor was I pushing my methods as the "correct" way more so things he could try himself easily as no one else was putting much out there. I agree that a live scanner and a experienced guy willing to use it(along with tradiotional tools) and invest some time is worth its weight in gold. I am lucky as because I know a lot of mechanics(some dealer guys too!!) I can usually get one (a live scanner) and some knowledge thats not charged per hour.


No explanations or apologies necessary Luke. I followed you to the "T" and your input was most benevolent. I can tell you've been around the toolbox a time or two in your experiences. The only thing more valuable than knowledge is the knowledge you gain from hands on experience. :salute:


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## B&B

Cosmic Charlie;803524 said:


> ANOTHER CLUE ?
> 
> when my 2004 HD 2500 is cold, I have a intake or exhaust noise (leak ?) that goes away when warmed up. I've heard stories about the intake manifold bolts being under torqued at the factory so not to damage the plastic intake housing ? any truth ?
> 
> is it related to highway speed flashing check engine light ?


 Could be either an intake or exhaust leak, just depends on the audible sound it makes. A constant ticking is an exhaust leak. A whistling sound that changes pitch at random is an intake leak. And either can cause a steady speed misfire, as both will affect fueling. Need to address that first before attempting to diagnose the steady speed misfire.

The common intake gasket specific leak is actually a combination of improper torque and a gasket that can not maintain it's clamp load...especially with a low initial torque spec. Both issues were updated eventually.

A small percentage of intake leak issues are also caused by the intake itself becoming warped along the gasket sealing surface from the low torque and several years of the under hood environment. But thats a far less common problem than the gaskets themselves. A gasket only replacement fixes them 95% of the time with no entire intake replacement necessary. In the event that a truck does need one Dorman makes a nice aftermarket one thats much more robust in the warp prone areas. In the few that I've needed I only used one OEM replacement, all others were Dorman as I feel theirs are a better design.


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## mkwl

B&B- after taking the truck out on the highway, I got the light to flash again. If I "punched" it with the light flashing, the truck still seems to fun fine. I also got it to come on running in Park at around 3,200RPM's. The light stayed on down to an idle- no really noticeable idle "roughness" and the truck still seemed to have adequate power. Any thoughts?

I will say that the "issue" seemed to start shortly after installing a K&N filter in my truck (drop-in). Is it possible that the MAF needs to be cleaned to resolve the problem? 
If so- what do I need/what is the proper procedure?

Also- when I was having an ABS issue with the truck (about 2MO ago), I had been disconnecting the battery from the truck a lot (maybe 12 times or so in about a 1 month window)- this is also about the time the issue came up. Could re-setting the computer so many times have somehow "confused" the truck's crank sensor and it would need to be reprogrammed?

Thoughts?


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## RichG53

Were is the MAF sensor located on the engine ???? I would like to see if mine needs cleaning.....
01-- 6.0


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## Luke_P

Matt, is it a paper filter? (drop in) or a oiled filter? Maybe you missed it as there are a lot of posts on here but 2cor has already said how to clean the MAF(1st page) and B&B mentions it in one of his last posts. Basicly spray it down good with MAF cleaner and don't touch the wire grid with anything. I would be suspicious of that filter or if you bumped\did something else by accident, when a problem shows itself right after you did something its usually related (but not always). 

I am sure you'll get a better response then this on the battery disconnection thing but its generally not a good idea, many shops connect a small power supply to your vehicle when dissconnecting your ground or replacing the battery so your computers "memory" is not lost.


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## mkwl

Thanks Luke- I assume that the MAF has to be removed then?

As for the computer- if anyone has any further thoughts on that, they would be much appreciated!


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## B&B

mkwl;804133 said:


> B&B- after taking the truck out on the highway, I got the light to flash again. If I "punched" it with the light flashing, the truck still seems to fun fine. I also got it to come on running in Park at around 3,200RPM's. The light stayed on down to an idle- no really noticeable idle "roughness" and the truck still seemed to have adequate power. Any thoughts?
> 
> I will say that the "issue" seemed to start shortly after installing a K&N filter in my truck (drop-in). Is it possible that the MAF needs to be cleaned to resolve the problem?
> If so- what do I need/what is the proper procedure?
> 
> Also- when I was having an ABS issue with the truck (about 2MO ago), I had been disconnecting the battery from the truck a lot (maybe 12 times or so in about a 1 month window)- this is also about the time the issue came up. Could re-setting the computer so many times have somehow "confused" the truck's crank sensor and it would need to be reprogrammed?
> 
> Thoughts?


Being that you can now make it flash the CEL light even with the truck stationary would make it easier to diagnosis with the scanner (and also likely rules out a fuel supply issue) but doesn't give me much to go on without scanner data.

Disconnecting the battery won't cause an issue like what your experiencing no matter how often or how many times you did. All it would do is wipe out any stored codes and freeze frame and stasis data for the emissions controls that could be viewed by the diagnostic tech. And now knowing that I'm sure its clear to you not to disconnect the power again for any reason until it's diagnosed. Otherwise it just makes the job tougher for the tech as there's no history to view in the ECM.

Disconnecting the power also doesn't affect the learned crankshaft value as it's flashed (burned) directly into the flash chip in the ECM. Only if you replace the crank, the engine or the ECM do you need to do a crank offset re-learn procedure. Even in the instances where it would need one there's a specific code stored in the ECM to let you know.

Go ahead clean the MAF, it's the cheapest and easiest thing you can do on your own and it's a maintenance item anyway. And be sure to tell the shop that you already did it as it's one of the first things they'll do to.


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## B&B

RichG53;804235 said:


> Were is the MAF sensor located on the engine ???? I would like to see if mine needs cleaning.....
> 01-- 6.0


Location is right near the airbox. 10 minute job even while being careful...as you should when working with a MAF.


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## Luke_P

matt as per B&B's pic hose clamps and a weatherpack connection(wiring harness). note orientation(just a good habit) remove, clean, allow to dry, reinstall. not a big deal. Any luck on finding a good local guy yet? if it gets to that.


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## Bajak

I pop the hood and check the engine. It's still there runs good. It's just a stupid light. Fill it with fuel and keep going. Still have 1968 vehicles on the road with out a dummy light. They just cause unjust worries. Breath easy and plant a tree.


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## Bajak

Pay attention to B&B not me. I only give my opinion. In my opinion he is next to God.


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## RichG53

Thanks !!! Those MAF'S are that sensitive ??? WOW !!!!


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## 2COR517

RichG53;804697 said:


> Thanks !!! Those MAF'S are that sensitive ??? WOW !!!!


Very sensitive. Use light hands when removing it. You won't be able to tell if it needs cleaning by looking at it. If you have more than 20K on the truck, clean it. Just grab a can of previousy mentioned CRC brand MAF Sensor cleaner at Napa or Autozone. You wont use it all, so hang on to it for next time.


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## RichG53

I bought the truck used so I don't know if any thing was done..... If it is dirty what will it affect??? Gas mileage ??? Or any thing else ?????


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## B&B

RichG53;804718 said:


> I bought the truck used so I don't know if any thing was done..... If it is dirty what will it affect??? Gas mileage ??? Or any thing else ?????


Gas mileage, performance and smooth operation throughout the RPM range.

One of the most important sensors for proper engine operation.


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## 2COR517

B&B;804833 said:


> Gas mileage, performance and smooth operation throughout the RPM range.
> 
> One of the most important sensors for proper engine operation.


I had a very noticable improvemant in all three when I cleaned mine. I also cleaned the throttle body at the same time.

Here's more details.

I can't seem to link the thread, but search for "induction". It should be at the top, started by me.


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## RichG53

So it's that honey comb ( mesh ) that needs to be cleaned correct ????? I did take a look at mine didn't notice any thing... But will look into cleaning it ...... Thanks !!!


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## 2COR517

The 2 1/2 (or five, depending on how you look at the world) small horizontal (in this picture) wires are the actual sensor. The honeycomb serves to smooth the airflow as it approaches the sensor, and to some degree protect the sensor. Say you forget your air filter and drive through a mountain of leaves or gravel.









I like to remove the four screws that sandwich everything together. This allows you to clean the inbound side of the MAF better. As previously mentioned, you won't be able to see anything on the wires, but clean them anyway.


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## 2COR517

Here's the induction system cleanup thread.

http://www.plowsite.com/showthread.php?t=82292&highlight=induction


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## SawHoss

Well, as I said before, my mechanic advised me to borrow a buddies MAF sensor, just to make sure that mine was the problem. Well, I borrowed it, and like every other trip on the highway over 70-75, the same symptoms happened, and the light turned on again. So, now I guess that my problem isnt the MAF sensor. If anyone else is going about the same problem as me (knowing for sure it isnt the MAF sensor) then any other input would be appreciated.


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## RichG53

2COR517's Avatar 
2COR517 2COR517 is online now
PlowSite.com Addict
I looked at the site... My truck is a little newer with 127,000 mi.... 
I have an 01 6.0 I would love for some one tell me all the things that need to be looked at... And the correct procedure to clean or tell me what should be done to them... On a regular schedule.... I use to own a 92 very simple to keep up with .....


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## B&B

RichG53;805219 said:


> I looked at the site... My truck is a little newer with 127,000 mi....
> I have an 01 6.0 I would love for some one tell me all the things that need to be looked at... And the correct procedure to clean or tell me what should be done to them... On a regular schedule.... I use to own a 92 very simple to keep up with .....


Following the severe maintenance recommendations and intervals will take care of most of it.

The rest...

MAF clean once a year or every 15K

Disassemble the brakes every two years or so in order to clean the rust buildup from the brake pad slide grooves in the caliper brackets (likely why you have the low pedal you mentioned).

1) If it still has Dexcool in it be sure to change it every 3 years MAX regardless of mileage. And if you have no idea when it was last done do it now.

2) Run a can of Sea Foam or Chevron's Techron fuel injection cleaner through it every 5K or so.

3) If you're still running Dexlll in the T-case be sure to check the oil level at least once a year or every 10K.

Everything else is obvious, just look things over, loose fasteners, excessive corrosion on anything critical, rusty brake lines, swelled hose, worn belts and all the other things too numerous to mention.


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## RichG53

B&B I am a look at every thing person ... When I see rust I go after it... I always check hinges nuts & bolts fluid levels etc ... I just am not used to the newer trucks... And all the things to check on a regular Necessity ....... Thanks !!!!!!!


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## mkwl

I'm not certain, but it seems like after running injector cleaner through a couple tankfulls the truck is doing better- the light seems to be coming on less often than it was before. Could the culprit be a (or more than one) clogging injector? Or is this just wishful thinking?


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## stillen

it most definitely could have been a dirty injector(s)..... $9 bux in injector cleaner sounds much better than a gasket or injector replacement.. Run some quality fuel through that puppy, keep us posted. I love to hear about cheap fixes


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## mkwl

Okay well I'm taking the truck downstate this weekend to do some excavation, so I'll have a good feel for if the truck's getting better or worse by then. 

For now, I'll run premium and some injector cleaner through it and see how it does...

Will keep everyone posted...


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## welded wrenches

was that check engine lite a miss print..or a g.m. typo error......maybe that warning light should have read (CHECK WALLET)


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## RichG53

B&B;805557 said:


> Following the severe maintenance recommendations and intervals will take care of most of it.
> 
> The rest...
> 
> MAF clean once a year or every 15K
> 
> Disassemble the brakes every two years or so in order to clean the rust buildup from the brake pad slide grooves in the caliper brackets (likely why you have the low pedal you mentioned).
> 
> 1) If it still has Dexcool in it be sure to change it every 3 years MAX regardless of mileage. And if you have no idea when it was last done do it now.
> 
> 2) Run a can of Sea Foam or Chevron's Techron fuel injection cleaner through it every 5K or so.
> 
> 3) If you're still running Dexlll in the T-case be sure to check the oil level at least once a year or every 10K.
> 
> Everything else is obvious, just look things over, loose fasteners, excessive corrosion on anything critical, rusty brake lines, swelled hose, worn belts and all the other things too numerous to mention.


 I have run sea foam in the tank how can I run it through the TB ???? The T-case oil was replaced last year.... Have to look into the Ant-freeze....


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## 2COR517

Rich, look at post 57 of this thread.


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## RepoMan207

mcginner;801393 said:


> When the engine light is flashing it means you are doing harm to the catalictic convertors which are very expense for those truck and have a chance of plugging up and cause your truck to run like a bag of crap.
> Get the truck check by a pro to see why the light is on. You most likily do need new plug & wire set, a fuel filter would be a good idea too.
> Also the oil from the K&N filter can cause problems with the MAF sensor. Clean the sensor with brake cleaner.


There is a MAF cleaner for that....If I remember right I was told the brake cleaner is too harsh for that application.


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## chevy5150

Has anyone ever tryed www.justanswer.com? For $9.00 you can talk to a ASE certified GM tech. If you had an intake gasket leak or vaccum leak you would most likely get another code ( lean code )after driving for this amount of time. Depends on how big. You can easily check for intake leaks with some flammable carb or brake clean. Wait for the engine to cool down. Fire it up and spray around the intake manifold and anywhere air may leak in. Try not to spray too much by the coils and wires as they can ignite the cleaner if you have a bad plug. If the cleaner leaks in the engine will rev up. Also replace the fuel filter. Its past due for one. Have you pulled the number one spark plug to see if it looks good?


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## B&B

Apparently some of you guys just hopping on do not bother to read all the posts...


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## RichG53

I read the post but I have an 01 not a 97 ... They are a little different... I don't have the vacuum line to pour it in to ......... Just wondering witch is the best way !!!!!


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## B&B

:waving: Wasn't geared specifically at you Rich but just follow 2COR's provided info as your truck is no different in the way you inject the cleaner.


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## RichG53

OK !! But were can I pour it into ?????? I don't see a vacuum line ....... I have one that goes to the power steering pump. from the master cylinder.....


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## 2COR517

Rich - from the last post of the thread I linked - 

..... For anyone else that is thinking of doing this, I did the SeaFoam through the intake again. I did it a little bit differently, with much more dramatic results. I poured the SeaFoam into the TB. Mostly in the IAC port on the backside of the TB. The IAC valve opening is quite small, so it makes quite a sucking sound. This really seemed to help atomize the SeaFoam better. As soon as it was in, I shut the truck off. Pulled the ECM fuses, and put the air inlet duct back together. You need to pull the fuses to clear the codes from running the truck without the MAF connected. Let the truck sit for an hour or better. This is a great time to change your fuel filter LOL. Started it up and took it for a ride. It took five miles before it stopped blowing black smoke

Its a good idea to clean the TB before you do the SeaFoam. The details are in the linked post.
It's pretty simple, good luck.


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## RichG53

THANKS !!!!!! I will follow your recommendations.......Just a thought can I pour the sea foam into the PVC hose ????


----------



## 2COR517

RichG53;810866 said:


> THANKS !!!!!! I will follow your recommendations.......Just a thought can I pour the sea foam into the PVC hose ????


You could, but you still should clean the TB and IAC.


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## Newdude

Hey B&B, could mkwl's problem be caused by a bad O2 sensor, thats throwing the wrong information to the PCM, causing the engine to react and then mis-fire??


----------



## B&B

Newdude;811111 said:


> Hey B&B, could mkwl's problem be caused by a bad O2 sensor, thats throwing the wrong information to the PCM, causing the engine to react and then mis-fire??


Not likely. More like one of the many other possibilities I already mentioned and needs the proper diagnosis to determine as mentioned.


----------



## mkwl

B&B;811136 said:


> Not likely. More like one of the many other possibilities I already mentioned and needs the proper diagnosis to determine as mentioned.


Could it be a dirty injector, and injector cleaner would be helping it (I could be wrong, but it seems to be doing a little better)?


----------



## B&B

mkwl;811249 said:


> Could it be a dirty injector, and injector cleaner would be helping it (I could be wrong, but it seems to be doing a little better)?


Sure Matt it's 100% possible it's suffering from restricted injectors. That was one of the possible causes I mentioned before.

Run a few cans of Sea Foam or Chevron's Techron FI cleaner through it if you want to try the low buck DIY approach. Can't hurt...


----------



## mkwl

B&B;811302 said:


> Sure Matt it's 100% possible it's suffering from restricted injectors. That was one of the possible causes I mentioned before.
> 
> Run a few cans of Sea Foam or Chevron's Techron FI cleaner through it if you want to try the low buck DIY approach. Can't hurt...


Thanks B&B- I'll keep running some more Techron through it and see how it does. I'm going on a 400 mile round trip with it this weekend so I'll see how she does and report back on Monday...


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## mkwl

Okay- well I drive the truck home on Friday- light came on like normal about every 20 miles or so. On the way up, I had my dad's scanner plugged into the truck, and we erased the DTC P0300 code before I left- light NIVER came on once the entire trip up! Any thoughts? Is it just dumb luck or could it haver been a computer glitch of some sort that the scanner solved?


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## B&B

Would just be a coincidence with the scanner. But possibly the FI cleaner you're running through it is helping. Continue to run it for a while and see how it goes.


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## 70monte

Did you ever clean the MAF sensor? I have not seen a post that says you did this.


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## mkwl

I'll keep running the FI cleaner through it- so far so good since the light didn't even come on once on the trip up yesterday (was at 65 or so for most of the trip)- will see how it does.

Is it possible that there could have been some kind of "computer glitch" which erasing the code solved?

As for the MAF- if it comes back on again, that will be the next thing I'll try.

Running the truck with the scanner, all the truck's "vital signs" looked normal- compared to out '01 Chevy Suburban 5.3L V8, very similar numbers, and all "seem" to be normal, so far so good...


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## brad96z28

What where the short term and long term fuel trim % ?


----------



## mkwl

brad96z28;814251 said:


> What where the short term and long term fuel trim % ?


Bank 1 Short: -.7 to 3.9.
Long: 12.3

Bank 2 Short: -3.9 to 4.6.
Long: 12.7.

I think the reason the bank 2 short had an outlier of -3.9 was because that was what the particular frame captured on the scanner, and just happened to be the one I recorded.

The check engine light did NOT come on during any of this scanner diagnostic testing...


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## brad96z28

Looks like its adding fuel on the long term . Ck engine light doesnt really matter It often times will not trip a code for a lean or rich condition until It has reached it maxium adapt of 25%. At 12 percent + long term If is adding fuel to make up for something somewhere. Did u mointor the short term fuel trims using live data if so what where they? Also on the misfire monitor screen on history misfires what where the readings and did it show any current misfires?


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## mkwl

brad96z28;814460 said:


> Looks like its adding fuel on the long term . Ck engine light doesnt really matter It often times will not trip a code for a lean or rich condition until It has reached it maxium adapt of 25%. At 12 percent + long term If is adding fuel to make up for something somewhere. Did u mointor the short term fuel trims using live data if so what where they? Also on the misfire monitor screen on history misfires what where the readings and did it show any current misfires?


Yes, compared to our suburban's long term, I would agree that it's feeding in more fuel than it comparatively should- it's on average putting in 12.65% at 24% throttle. Both banks are near the same though- which would lead me to think it might be starving for air somehow- perhaps something to do with the MAF (which may need cleaning)? Would the MAF not allowing enough air into the system cause the long term banks % to be elevated from normal?

On the misfire screen, it showed one past misfire- both banks were the same as the data here, but for some reason the truck showed the scanner that it was at only 4% throttle cruising at 70MPH on the highway (when the CEL was tripped- flashed, then went off)...???? For now, the light's off- I'm open to ideas....

What's a "normal" long term % for each bank on these trucks (Vortec 6000 with the 4L80E and 4.10 rearend?


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## B&B

Matt your LTFT's of +12.3 and +12.7 are not the out of line for a 6.0 of higher mileage...and it's definitely not compensating for a sever lean condition of major magnitude but you may have a small one. 

However they are high enough to suspect that the MAF is sending errored data, quite possibly from a dirty MAF or you have an intake leak. Wasn't aware that you haven't yet cleaned the MAF. Be sure to do so before you do ANYTHING else.

Once you have it cleaned; disconnect the battery for a few minutes to reset the fuel trims, drive it at least 30-40 miles and then re-monitor the LTFT's again...checking to see if they've reduced closer to the zero cross threshold. Let us know what you find...


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## mkwl

Thanks for the input B&B, I will be home again the weekend after next, when I have the truck home I'll get the MAF cleaned and report back. For now, I'll see how she does...

Thanks!


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## RichG53

2COR517;810578 said:


> Rich - from the last post of the thread I linked -
> 
> ..... For anyone else that is thinking of doing this, I did the SeaFoam through the intake again. I did it a little bit differently, with much more dramatic results. I poured the SeaFoam into the TB. Mostly in the IAC port on the backside of the TB. The IAC valve opening is quite small, so it makes quite a sucking sound. This really seemed to help atomize the SeaFoam better. As soon as it was in, I shut the truck off. Pulled the ECM fuses, and put the air inlet duct back together. You need to pull the fuses to clear the codes from running the truck without the MAF connected. Let the truck sit for an hour or better. This is a great time to change your fuel filter LOL. Started it up and took it for a ride. It took five miles before it stopped blowing black smoke
> 
> Its a good idea to clean the TB before you do the SeaFoam. The details are in the linked post.
> It's pretty simple, good luck.


 If you pour it into the IAC do you need to disconnect the MAF sensor ???? It is down stream ... I want to do it through the IAC do I need to disconnect the MAF sensor ????


----------



## 2COR517

Rich - you need to disconnect the MAF because you need to remove the fresh air tube on the top of the TB. You're not going to remove the IAC, just pour it in where the IAC draws fresh air from. When you look at the top of the TB, at the back there is a smallish opening, maybe 1/4" by 3/4". This is where I dumped it in. I don't have a pic handy, I'll try to get one tonight. If you remove the TB to clean it, it will make sense.


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## RichG53

I did remove it(TB)and cleaned it but did not notice the small opening ... Some pics would help Thanks !!!!! I have an 01 6.0......


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## RichG53

QUOTE=RichG53;814751]OK!!! B&B you recommend changing O2 sensors every 100,000 I have over 127,000 mi. How can I tell if they may have been changed when I bought the trk with 115,00 on it ??? Is there some way to tell if they have been done ???? Or if they need ti be done ???
Thanks !!!! Rich .....[/QUOTE]
This is some thing from another part of the post(Induction cleaning) that I need an answer to ....
Thanks !!! Rich...


----------



## RichG53

2COR517;814739 said:


> Rich - you need to disconnect the MAF because you need to remove the fresh air tube on the top of the TB. You're not going to remove the IAC, just pour it in where the IAC draws fresh air from. When you look at the top of the TB, at the back there is a smallish opening, maybe 1/4" by 3/4". This is where I dumped it in. I don't have a pic handy, I'll try to get one tonight. If you remove the TB to clean it, it will make sense.


One more question ... Do I need to pull the ECM fuse after or before doing this cleaning??? To rest any codes .....If so how long before restoring power to fuse for ECM ?????


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## 2COR517

Pull the ECM fuses after drawing the SF in. Let the truck sit for an hour or so, put the fuses in, take her for a ride.


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## RichG53

I still need some answers to the 02 sensor question no.95... Thanks !!!!


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## RichG53

Thanks 2COR517....I would like to see pics of the hole.......I still need some answers to question NO.95 ... On 02 sensors .... Thanks !!


----------



## B&B

RichG53;814851 said:


> Thanks 2COR517....I would like to see pics of the hole....


Not so sure I like the sound of that. 

Here's what you want to be sure you get clean....


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## 2COR517

Rich, the spots B&B circled are where you can pour the SeaFoam in. Glad he posted that pic, mine is slightly different.


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## brad96z28

If it does have an air leak It should be showing up on stft at idle. Ur not gona notice much of a vac leak at cruising speeds on a scanner, a lean condition during cruising would be more in line with a faulty maf.Aparently some people have had a heck of alot better luck cleaning a maf then I have. I have had to replace several in the last month.It may be a good maitnence thing but dont put much faith in it solving any problems. I would stil try cleaning it and borrowing another if need be.


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## B&B

Not if it's raised the LTFT's to the next fueling cell already and started the STFT's back to zero. Which is exactly what they do after enough time has passed. And with LTFT's over 10% it's a near guaranteed bet that it's already past that point. STFT's are not the only limited to idle conditions, they are simply a fine tune of LTFT's which as you know are used across the entire operating range.

Whole reason you reset them by disconnecting ECM power after making a repair or to further test your diagnosis.

Fixed many-a-issues with nothing more than a good MAF clean. Especially so on a high mileage unit running on E10 these days. But yes from time to time there's no replacement for a replacement.


----------



## RichG53

What are you referring to ?? LEFT'S & STEF's .... And how do they affect MPGS or any thing else ??? Thanks ! ! ! !


----------



## B&B

RichG53;815500 said:


> What are you referring to ?? LEFT'S & STEF's .... And how do they affect MPGS or any thing else ??? Thanks ! ! ! !


STFT = Short Term Fuel Trims.
LTFT = Long Term Fuel Trims

Fuel trims refer to adjustments being made dynamically to the base fuel table to get the proper ratio of fuel to air. Short term fuel trim refers to adjustments being made in response to temporary conditions. Long term fuel trim is used to compensate for issues that seem to be present over a much longer period. Fuel trims are expressed in percentages from zero....positive values indicate that the ECM is seeing a lean condition (so it's adding fuel) and negative values indicate a rich condition ( so it's subtracting fuel). both the ST and LT trims are calculated by using a wide set of data values from various sensors such as the O2 sensors, intake air temperature, MAF sensor, engine coolant temp, engine load, throttle position (and change in throttle position), and even battery voltage in some cases. Long term fuel trims generally shouldn't exceed +- 10% but with todays widespread use of E10 fuel most pre- '03 vehicles will show a minimum of +5% LTFT's as it's compensating for the lower air/fuel ratio of the E10 over straight gasoline that it wasn't originally designed to be operated on. Short terms you always want as near zero as possible but + or - 2% would be considered as normal and wouldn't be indicative of another issues.

Both the ST and LT fuel trims are cell based, meaning that they use a matrix based on RPM and load (determined from the MAP sensor) to determine which "cell" of the fueling table the engine is operating in. Each cell can store its own fuel trim correction and under normal driving with open throttle the ECM uses several of these "cells" to determine what the fueling SHOULD be, referencing MAP voltage and MAF values against RPM's. It basically uses low RPM (below approx 2K RPM) and high (above approx 2K RPM), referenced against 6 different MAP voltage set points to decide what should be the correct fueling for that given load and condition. So as an example, if you had a LTFT correction of +15% it would be adding 15% more fuel than what should have been required as deemed by the programming in the ECM. So basically the LTFT & STFT are the fueling corrections that the PCM is adding/subtracting to the base fueling calibrations to add or remove fuel based on sensor feedback. STFT's are the "on the spot" temporary changes of up to 25% correction to add or remove fuel. If the PCM continually has to add 10% more fuel via STFT's under certain operating conditions/ranges, the LTFT's would then come into play and would be adjusted so the STFT can get back towards the zero correction that it's trying to, as the PCM always wants the STFT as close to zero correction as possible, but again with E10 that won't always happen. So, with knowing this info and in Matts case there's a good chance you'd be looking for a vacuum leak, a weak fuel supply or some erroneous data from a sensor that has a direct impact on the fueling parameters of the engine (such as a contaminated MAF) thats showing the ECM a lean condition.

LT and STFT's won't affect MPG's unless there's another issue thats falsely calling for an increase of fuel trims...if they're in spec and fueling as intended.


----------



## RichG53

B&B WOW !!! Can I take you to Washington and show them. what this Ethanol is doing to confuse these older vehicles... I wish you lived closer.... I would love to sit down and talk about all the things you KNOW. I do know a lot but always want to learn more ...
I love learning..... PCM I know what that is suppose to stand for but can't come up with it...Can you refresh me ???? What could throw off MPG"S ????? (with these trims).. I am anaul about getting the most out of my truck ..(MPG'S or any thing else that makes them run at peak performance )... THANKS ! ! ! ! !


----------



## 2COR517

Powertrain Control Module.

Sorry, but the excess punctuation is giving me a headache. Literally.


----------



## RichG53

Thanks ! !


----------



## B&B

Faulty sensor data feedback to the PCM and poor tuneup routines are the main killer for max MPG's. 

Do and follow the procedures we've spoke of over the last few weeks in the various threads and you'll be doing everything you can to get maximum life, performance and MPG's from your truck.


----------



## RichG53

Can you tell me were the PCM sensor is located so I can check it .....Also what should I be looking for ????
Thanks ! !


----------



## 2COR517

The PCM is the brains of the operation. It receives data from dozens of sensors throughout the vehicle. Throttle position, MAP, MAF, crank/cam position, coolant temp, oil pressure, vehicle speed, oxygen sensors, etc. The PCM then uses this data to command fuel rates, spark timing, shift points, IAC, etc.

If you look around there are some good books available on engine/fuel/emissions management. Even AutoZone has some I believe. It would be worth it for you to pick one up and read it through. Many more of the posts/replies would make much more sense to you.


----------



## RichG53

Thanks !! I will look in to that .........


----------



## mkwl

Okay- well I drove up to our camp today with the truck- about a 100 Mile trip on the highway (65-68MPH), CEL came on again (flashing) 3 times- twice with 3-5 flashes, and once with 20 flashes. The scanner for some reason (had it hooked up to the truck to "record live data triggered by the DTC), didn't "trip" to record- so I have no data stored to look back on :realmad: . Anyhow, I'm thinking that the next "step" for me is to give cleaning the MAF a shot.

Just so I'm clear on the correct procedure:

1) remove the airbox and the sensor itself.
2) Take the sensor, and spray CRC MAF cleaner onto it, let it airdry (for an hr or so).
3) Install it back into its position.
4) Disconnect the battery for a few mins, reconnect- and see if anything has changed.

I know this has been outlined before, but I want to make sure I don't screw it up, and be kicking myself later for not asking for a confirmation of the correct procedure 

One aside- it seems like the CEL "likes" to come on more after I fuel up (with sunoco or mobil 89 octane fuel)- is is possible that the fuel could have some water in it and be throwing the P0300 DTC? Or is this more unlikely?


----------



## brad96z28

Its not ur fueI.U still have not done anything with the maf? I give up!


----------



## 2COR517

MAF is real easy to clean. Pull your ECM fuses. Disconnect the wires to it first. Take off the two clamps holding the MAF assembly in place. I pulled the four Torx screws from the adapters so I could clean the inbound side better. The honeycomb makes it tough otherwise. Give the wires a good spraying. Don't touch the wires with anything. No Q-tips, brushes, fingers, compressed air, the spray nozzle, NOTHING. Did I mention don't touch the wires? Let it dry a few minutes and put it all back together. Put your ECM fuses back in and you should be good to go.

What are you using for an air filter?


----------



## azandy

In the 70's we would change plugs,wires,cap, points and condensor. In the 80's we would change plugs,wires,cap,and rotor then pull the check engine bulb out. In the 90's we would open the hood and then proceed to put a piece of black tape over the light. Now, don't even look, just bring it in


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## mkwl

2COR517;823436 said:


> MAF is real easy to clean. Pull your ECM fuses. Disconnect the wires to it first. Take off the two clamps holding the MAF assembly in place. I pulled the four Torx screws from the adapters so I could clean the inbound side better. The honeycomb makes it tough otherwise. Give the wires a good spraying. Don't touch the wires with anything. No Q-tips, brushes, fingers, compressed air, the spray nozzle, NOTHING. Did I mention don't touch the wires? Let it dry a few minutes and put it all back together. Put your ECM fuses back in and you should be good to go.
> 
> What are you using for an air filter?


Thanks- I'm running a K&N right now- though after cleaning the MAF and seeing what that does for me I will go to a paper filter instead.


----------



## mkwl

azandy;823439 said:


> In the 70's we would change plugs,wires,cap, points and condensor. In the 80's we would change plugs,wires,cap,and rotor then pull the check engine bulb out. In the 90's we would open the hood and then proceed to put a piece of black tape over the light. Now, don't even look, just bring it in


Brought it in- dealer couldn't figure it out either


----------



## mkwl

Okay- will be cleaning the MAF tomorrow.

On the trip home tonight- I had my Dad ride with me to watch the scan tool's data. We noticed that the truck really only has the light come on (flashing), when I'm on a level road surface, or going down a gradual hill, with the speed between 63-73MPH. We also noted that we can almost "predict" when the light will come on- be it cause or effect, that when the vacuum and MAF intake are in a 2:1 or lesser ratio (with the vacuum being the larger number)- the CEL will usually trip- this is usually the case (99% of the time) going down a hill or on flat- with my foot out of the gas. 

Everything else looks fine with the light on- no numbers way out of whack, and the truck still runs pretty much fine with the light flashing... 

Anyhow- will try cleaning eh MAF and see what that does...

Also- does anyone know if the MAF off a '01 Chevy Suburban with the 5.3L V8 is the same as my truck? Could they be swapped?


----------



## mkwl

Okay- cleaned the MAF- no luck- still comes on at 2,800 or higher RPM's.
Swapped in another MAF identical part #- same thing.
Swapped in air ducting- same.

Thoughts? I really want to get this taken care of as it seems to be getting "worse", so I think I'm off to the stealer tomorrow :crying:

I will say though- it doesn't seem to come on as much/at all when it's raining outside or the air is warmer/moist- anything this could effect?


----------



## B&B

Still get the same P0300 and nothing else Matt?

Does your truck have an EGR on it? By '03 most didn't but there were some that slipped through.


----------



## mkwl

B&B;827164 said:


> Still get the same P0300 and nothing else Matt?
> 
> Does your truck have an EGR on it? By '03 most didn't but there were some that slipped through.


Same code and no others.

How would I know if it has an EGR?

I had one other thought- I hadn't installed AC-Delco plugs/wires- could it be that I have a faulty plug/wire or two?


----------



## Cosmic Charlie

my 2004 HD 2500 6.0 has had the problem for 3 + years, even after I changed the plugs a year ago ...


----------



## RepoMan207

This may be out in left field here......I had an issue with my truck last year 02 GMC 2500 HD 6.0....Mike you may remember this from a post from a certain other place. It caused some false reads on the scanner a few times, I did however catch up on some much needed maintenance. It turned out to be chaffing wires on the back side of the bell housing. I saw the exact same thing happen on friends truck over the summer (04 GMC 25000 6.0). Maybe it is worth a look. I thought I should throw that out there just in case. Good luck!


----------



## B&B

mkwl;827351 said:


> Same code and no others.
> 
> How would I know if it has an EGR?


Well since my post didn't get moved to the correct thread I guess I'll have to do it again, thanks guys.

Matt, look on the engine where shown in the pic for an EGR. It's easy to spy the tube traveling down to the exhaust manifold as well. Your truck equipped with it? If so, can you view the activity of it with the scanner you're using?









Also I was under the impression that you already changed the plugs. If they have plenty of miles on them it's not a bad idea regardless of having an issue or not. The wires will normally last 100K no problem.


----------



## 2COR517

Hey B&B,

Do you really have to remove all that sheet metal to do a tuneup on those?


----------



## mkwl

B&B;829715 said:


> Well since my post didn't get moved to the correct thread I guess I'll have to do it again, thanks guys.
> 
> Matt, look on the engine where shown in the pic for an EGR. It's easy to spy the tube traveling down to the exhaust manifold as well. Your truck equipped with it? If so, can you view the activity of it with the scanner you're using?
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Also I was under the impression that you already changed the plugs. If they have plenty of miles on them it's not a bad idea regardless of having an issue or not. The wires will normally last 100K no problem.


Thanks B&B- I'll check for the EGR after class- I don't think I've got one but I'll check.

I had changed the plugs, but not with AC/DELCO plugs/wires. Could it be a bad plug/wire causing the very slight misfire at high speeds? Would it pay to have my injectors cleaned?


----------



## 2COR517

What kind of plugs did you put in? What gap did you set them at?


----------



## mkwl

Nope- no EGR that I can see on my truck.

Plugs- ones the napa guy recommended (not AC Delco though- probably my first mistake). 
Gap- don't remember off hand- but it was what my owners manual spec'd.

Thanks guys- please keep the thoughts coming!


----------



## B&B

mkwl;832130 said:


> Plugs- ones the napa guy recommended (not AC Delco though- probably my first mistake).
> Gap- don't remember off hand- but it was what my owners manual specs.


Yep that would be a mistake. Nothing works better than the Delco 41-985's gapped to .040 in a 6.0. Since that's what they were designed for.

Get that taken care of before you do anything else.


----------



## Joesno

My truck does the same exact thing on the highway when i go 70mph and above. ive got an 03 2500hd 6.0 as well.


I told my dad about it and he said well dont go 70 and theres no problem. But its really anoying and starting to bother me.

i can ignore it either because something could be wrong.

i think ill hold off on getting this checked out till this thread has been solved.


----------



## mkwl

Okay- will be swapping in ACDelco plugs/wires and see what that does for me- thanks B&B.


----------



## mkwl

Okay- changed in ACDelco plugs, ACDelco wires, and took it to the dealer to have the fuel induction system cleaned- so far so good- haven't had a chance to get it above 60MPH, but the light is off as of now (knock on wood)...could it have been bad plugs/wires? It seemed to do it mostly when I was going DOWN a slight hill on the highway- any corroilation with plugs or wires?


----------



## RichG53

What would the EGR have to do with this problem ??? Is there a regular maintenance plan to do with the ERGs ????


----------



## mkwl

RichG53;839391 said:


> What would the EGR have to do with this problem ??? Is there a regular maintenance plan to do with the ERGs ????


Does your truck have an EGR on it? I'd be interested to know as well, also, why the newer trucks (I guess '03 and up) don't have them- what is their function?

Our chevy suburban has one (I believe)- anything to be done to keep the EGR going?


----------



## Newdude

mkwl;839444 said:


> Does your truck have an EGR on it? I'd be interested to know as well, also, why the newer trucks (I guess '03 and up) don't have them- what is their function?
> 
> Our chevy suburban has one (I believe)- anything to be done to keep the EGR going?


EGR is Exhaust Gas Recirculation. It takes exhaust gases, which are inert, and recirculates them back into the intake. The inert exhaust gases help to keep combustion temperatures down.


----------



## RichG53

RihG53;839391 said:


> What would the EGR have to do with this problem ??? Is there a regular maintenance plan to do with the ERGs ????


Yes I have one that is why I asked ...... Is there any maintenance that needs to be done to them ????


----------



## B&B

No real PM on an EGR. It works until it fails and is one of those things you don't touch unless it has an issue.


----------



## mkwl

B&B;839698 said:


> No real PM on an EGR. It works until it fails and is one of those things you don't touch unless it has an issue.


Thanks B&B- how come the newer engines don't have them?


----------



## B&B

Because they're more efficient with their emissions...or lack of. Through newer engine designs, more sophisticated programming and software the manufactures can reduce emission output by finely controlling both the fuel and spark of the engine to either reduce emission production directly or to better control it once it's produced. And in addition the cats are also far better at their job of cleaning exhaust output on the '03-current vehicles as well. All these together allows manufactures to be less dependent on EGR systems to make the engines compliant to emission regulations.


----------



## BigLou80

B&B;839726 said:


> Because they're more efficient with their emissions...or lack of. Through newer engine designs, more sophisticated programming and software the manufactures can reduce emission output by finely controlling both the fuel and spark of the engine to either reduce emission production directly or to better control it once it's produced. And in addition the cats are also far better at their job of cleaning exhaust output on the '03-current vehicles as well. All these together allows manufactures to be less dependent on EGR systems to make the engines compliant to emission regulations.


I have an '02 and I am 99% sure it has no EGR on it so they must have started deleting them before '03


----------



## B&B

BigLou80;839934 said:


> I have an '02 and I am 99% sure it has no EGR on it so they must have started deleting them before '03


They did. '02-'03 was the change over model years. It also depends on where the original delivery destination was intended for the vehicle. Virtually all California emissions vehicles still had an EGR for example.


----------



## mkwl

Okay- makes sense to me...I'm wondering though- sort off off-topic, but why do engines' emissions start to "increase" with mileage/age? Is it just things wearing out?


----------



## B&B

Things simply wear out with age and use. Engine tolerances loosen up, emission devices become less efficient as mileage increases etc. But with todays modern designs it's not nearly as much an issue as it once was. A 5 year old engine of today will still easily pass an emission test and still be drum tight with 100K on the clock in comparison to an engine of 20 years ago for example. Some things really are built better these days.


----------



## ibew697

Going to have to subscribe to this thread...my 03 2500HD 6.0 is throwing the flashing engine light @ 72-77 mph. It happened one time about a month ago and just decided to do the tune up on it and never really thought about it again UNTIL tonight when traveling down the highway for about 25 miles in the mid 70's and blam, it was back. I'll have to throw the POS K&N Filter in the garbage and clean the MAF. Hopefully it will correct my problem....Jake


----------



## mkwl

This seems to be a rather common issue with the '03 Vortec 6000 engines...hmmmm....


----------



## 2COR517

Matt - are you running a paper filter?


----------



## Diemaker

Disassembled the MAF sensor today and cleaned it with the CRC brand spray cleaner and no more service engine soon light. Thanks for the tip. It worked great and was very easy to do.


----------



## mkwl

2COR517;840336 said:


> Matt - are you running a paper filter?


Negative- have a K&N in it right now, will try and swap it for a paper one as soon as I have some more $$$ to spend...:waving:


----------



## dj89

Would crc throttle body cleaner be ok, or should i wait to the am and get the MAF cleaner.....


----------



## B&B

Do NOT use TB cleaner on a MAF.  Use the correct cleaner.


----------



## dj89

k Its all wal fart had, guess i can clean the Tb now ;-)


----------



## 2COR517

Napa or AZ will have MAF cleaner. Cleaning the TB is a very good idea.


----------



## Cosmic Charlie

BUMP / TTT

Still no solid answer !!!!

my 04 2500 HD Gas does the Flashing Check Engine Light even in my driveway in neutral when rev'ed to about 2500 to 3000 RPMs, and stops and the light goes out at idle 

WTF - Engine Miss Fire - But runs excellent

It's been doing it for years, I don't drive on the highway so otherwise it's fine with 101,000 miles

Wish I could find out ??????????


----------



## BigLou80

any one given any thought to the misfire sensor giving a false reading? IE detecting a misfire when there is not one ?


----------



## mkwl

Could be a bad sensor perhaps- that's what I'm thinking, since it seems that all the '03, 04's and '05's with the light flashing issue all run fine- even with the light on?!?!

B&B- thoughts?


----------



## fireball

Really interesting all this information. Thank you. What is the procedure for removing the flashing light other than using the ice pick through its heart trick.


----------



## Seaway25

mkwl;856783 said:


> Could be a bad sensor perhaps- that's what I'm thinking, since it seems that all the '03, 04's and '05's with the light flashing issue all run fine- even with the light on?!?!
> 
> B&B- thoughts?


My '01 does it too. Runs great though.


----------



## mkwl

Hmmm... so it would seem then that the older generation Vortec 6000 series engines have this condition....hmmmmm...


----------



## B&B

Trucks over 8600 GVWR do not use overly sensitive misfire or emissions monitoring calibrations. In fact they're MUCH less sensitive than trucks built with a lighter GVWR. If it's detecting misfires then it's detecting misfires, whether you can physically feel them or not. The problem is thats there's a thousand things that can cause them. Everything from the things I've previously mentioned before all the way to shoddy wiring add ons...to believe it or not aftermarket alarm and remote start systems.


----------



## mkwl

B&B has spoken- I'd trust his words of wisdom- got my injectors cleaned at the dealer a while back- so far so good- we shall see...


----------



## Cosmic Charlie

B&B;857627 said:


> Trucks over 8600 GVWR do not use overly sensitive misfire or emissions monitoring calibrations. In fact they're MUCH less sensitive than trucks built with a lighter GVWR. If it's detecting misfires then it's detecting misfires, whether you can physically feel them or not. The problem is thats there's a thousand things that can cause them. Everything from the things I've previously mentioned before all the way to shoddy wiring add ons...to believe it or not aftermarket alarm and remote start systems.


About 1000 things !!!!!!!

That's why mine has been flashing for 3 years on & off

my ase mechanic told me long ago: where do you want me to start and how much do you want to spend before I give up ?

I drove on the highway today & NO flasing light, for today anyway - Mines intermittent


----------



## hawk2wp

*02 gmc 2500 hd*

I have read most of this tread and cut and pasted much of B&B's advice ( thanks B&B) to try and resolve my problem. I have a 02 2500 HD 6.0 56,000 miles. Check engine light has been flashing intermittently the past year or more when I'm on the highway at 70mph or so. A new problem last week. Went to the drive through car wash and they sprayed a lot at the base of the windshield because there were leaves stuck there. My truck started missing shortly there after and the check engine light flashing at low speeds. Idle was rough. It cleared up through out the afternoon as I was running errands and made about 10 stops and starts over a 3-4 hour period. Next day pulled a trailer with scrap metal to the junk yard and everything seemed to be fine. I drove it yesterday and it was fine until I gunned it and was going up a hill and then it started running rough and the check engine light flashing again. Idling rough again. Only code is the P0300. I removed the #7 plug and it is dark and I pulled the #4 plug and it looks light tan which looks normal to me. ????


----------



## RichG53

Tan is GOOD !!!


----------



## B&B

Good chance it needs a fresh set of wires.


----------



## hawk2wp

I reinstalled the plugs and ran the truck for about 10 minutes. Used my infrared thermometer and found the #7 exaust mainifold to be much cooler then the others. I have a spark detector about the size of a ink pen. You just hold it against the spark plug boot and it shows if it is firing. #7 had no spark. I replaced the coil pac and everything is great now! Thanks for the help guys.ussmileyflag


----------



## RichG53

AMEN !!! AMEN !!!
Glad your good to go !!!!!


----------



## welded wrenches

*check engine light mis-print??*

i believe there is a mis-print on the light that says ;;check engine;; it should actually say ;;;check your wallet;;


----------



## vttruck

I've got an 02 2500HD 6.0L with 97k and have had from day 1. I've been living with the flashing CEL for a couple of years after trying several trips to the dealer. Checking it with an Autozone scan tool shows P0300 random/multiple misfires. I've had the TB cleaned, GM fuel injector treatment(2 or 3 times), changed 2 coil packs on the originally offending cylinders (dealer diagnosed #3, #6 at 2 different dealers, months apart), all new plugs, checked the continuity of all plug wires, just cleaned MAF for the first time, checked vac hose on FPR - no fuel present, new paper air filter - had K&N for 95% of these miles.

Originally I didn't notice the misfire, but lately it's been worse. I can feel it on the highway badly. Fuel economy is worse, and seems the problem is getting worse. Don't want to throw parts at this thing, but my frustration level is boiling over.

Is it possible for MAF to be bad? If so, any way to know?

Haven't changed intake manifold gasket yet, could this be the cause?

Here's a sample of the freeze data from different days, both dry outside, but first two 47 F(same day), third 30 F.

Throttle Position: 25 33.3 21.1 %
Engine RPM: 2451 2652 2397
Load Value: 19.2 28.2 15.2 %
Air Flow Rate: 54.12 79.63 43.02 GR/SEC
MAP Sensor: 60 79 52 kPa
Coolant Temp: 190 194 194 F
STFT1: -1.0 3.9 5.4 %
LTFT1: 9.3 13.2 8.5 % 
STFT2: -3.4 0.0 0.8 %
LTFT2: 9.3 13.2 8.5 %
STFT3: -80.1 32.0 14.8 %
LTFT3: 64.8 24.2 0.0 %
STFT4: -67.4 57.0 -89.7 %
LTFT4: 70.3 8.5 35.9 %
Speed: 47 49 47 MPH


----------



## mkwl

vttruck;909462 said:


> I've got an 02 2500HD 6.0L with 97k and have had from day 1. I've been living with the flashing CEL for a couple of years after trying several trips to the dealer. Checking it with an Autozone scan tool shows P0300 random/multiple misfires. I've had the TB cleaned, GM fuel injector treatment(2 or 3 times), changed 2 coil packs on the originally offending cylinders (dealer diagnosed #3, #6 at 2 different dealers, months apart), all new plugs, checked the continuity of all plug wires, just cleaned MAF for the first time, checked vac hose on FPR - no fuel present, new paper air filter - had K&N for 95% of these miles.
> 
> Originally I didn't notice the misfire, but lately it's been worse. I can feel it on the highway badly. Fuel economy is worse, and seems the problem is getting worse. Don't want to throw parts at this thing, but my frustration level is boiling over.
> 
> Is it possible for MAF to be bad? If so, any way to know?
> 
> Haven't changed intake manifold gasket yet, could this be the cause?
> 
> Here's a sample of the freeze data from different days, both dry outside, but first two 47 F(same day), third 30 F.
> 
> Throttle Position: 25 33.3 21.1 %
> Engine RPM: 2451 2652 2397
> Load Value: 19.2 28.2 15.2 %
> Air Flow Rate: 54.12 79.63 43.02 GR/SEC
> MAP Sensor: 60 79 52 kPa
> Coolant Temp: 190 194 194 F
> STFT1: -1.0 3.9 5.4 %
> LTFT1: 9.3 13.2 8.5 %
> STFT2: -3.4 0.0 0.8 %
> LTFT2: 9.3 13.2 8.5 %
> STFT3: -80.1 32.0 14.8 %
> LTFT3: 64.8 24.2 0.0 %
> STFT4: -67.4 57.0 -89.7 %
> LTFT4: 70.3 8.5 35.9 %
> Speed: 47 49 47 MPH


I'd give cleaning your MAF a shot- I feel your frustration- took me 3 trips to the dealer to get it resolved (I think).... plugs, wires, and a fuel injection flush- had it done 2 months ago- so far (knock on wood) the light has stayed off... now that I say this it'll probably start flashing again :crying:

I'd use some CRC MAF cleaner- and see what that does for you...


----------



## vttruck

I cleaned the MAF with the CRC MAF cleaner. No change, CEL keeps flashing. Other possibilities?


----------



## dsimo

FYI, same issue with the CEL over 60 MPH. Tried tune-up, new intake gasket, swapped out mass airflow. Nothing changed. One Tech told me to relearn the crank sensor, haven't done it yet but that is the next step. Will post again when I find a solution, or if someone beats me to it that would be fine to.


----------



## Cosmic Charlie

My guess (again) is an intermittently bad coil pack ....

In park rev motor to 2500 or more for 30 seconds (or more) and see if the CEL starts flashing, if so have some continue to rev engine and check the coils ...

Thats how I found mine.

Though each problem may be different ...


----------



## vttruck

I have done this before and yes in park revving the engine causes the CEL to flash. 

Previously, at idle, I pulled the plug wire off each coil and they all were sparking.

I'm assuming the spark means they're good. 

I'll try checking again with the engine at 2500 RPM. Hopefully I'll find something.

Thanks for the post.


----------



## mkwl

Does anyone think it possible that the new E10 fuels could be causing varnish deposits (on trucks from say '05 and older) to go through the fuel filter, and in turn clog up the injectors? I had my injectors cleaned, and so far (knock on wood) so good... thoughts?


----------



## B&B

The alcohol content of E10 itself isn't responsible for creating varnish, however what it will do is loosen in an attempt to remove any that may be present in the system already but that would have already taken place in a matter of the first few tankfuls it doesn't contribute to the actual formation of it. And once the varnish was "washed" through the system it remains in a liquid state anyway so there's really no way for it to clog anything or cause any noticeable issues due to it.

What it is tough on however is any rubber or plastic components in the system on vehicles built prior to the mainstream use of E10. It also affects fuel mileage (due to less BTU content than 100& gasoline) and absorbs water easier. And it's the water buildup that can be tough on fuel pumps manufactured during pre-E10 era for example.


----------



## mkwl

B&B;962457 said:


> The alcohol content of E10 itself isn't responsible for creating varnish, however what it will do is loosen in an attempt to remove any that may be present in the system already but that would have already taken place in a matter of the first few tankfuls it doesn't contribute to the actual formation of it. And once the varnish was "washed" through the system it remains in a liquid state anyway so there's really no way for it to clog anything or cause any noticeable issues due to it.
> 
> What it is tough on however is any rubber or plastic components in the system on vehicles built prior to the mainstream use of E10. It also affects fuel mileage (due to less BTU content than 100& gasoline) and absorbs water easier. And it's the water buildup that can be tough on fuel pumps manufactured during pre-E10 era for example.


Any good way to combat the damage potential from E10? I assume my '03 is really before the widespread use of E10, right?


----------



## B&B

Just keeping the fuel fresh and flowing is the #1 important thing as it can absorb moisture and also breakdown faster than regular gasoline. It was always preached the straight gasoline had a shelf life of approx 6 months if stored correctly but E10 can have a self life of as little as 30 days and up to 90 days in ideal conditions. 

Thats about the best you can do. However your '03 would be E10 compatible in it's components so there's nothing else or "special" that would be needed to prevent any additional issues from happening to it specifically.


----------



## mkwl

B&B;964485 said:


> Just keeping the fuel fresh and flowing is the #1 important thing as it can absorb moisture and also breakdown faster than regular gasoline. It was always preached the straight gasoline had a shelf life of approx 6 months if stored correctly but E10 can have a self life of as little as 30 days and up to 90 days in ideal conditions.
> 
> Thats about the best you can do. However your '03 would be E10 compatible in it's components so there's nothing else or "special" that would be needed to prevent any additional issues from happening to it specifically.


Okay thanks- I run through about 1/2 tank per week- so there's almost always new fuel in 'er. What year (and back) would vehicles not be really be okay with E10?


----------



## B&B

'02 and prior Matt. And if you think about all you've heard about early fuel pump deaths on vehicles it makes prefect sense; because they were notorious for dying early, and most were and are on pre-'03 models. And it's mainly due to the incompatibility with ethanol fuel. By '03 they (the vehicles) were at least partially ready for it and it's widespread use.


----------



## mkwl

B&B;964537 said:


> '02 and prior Matt. And if you think about all you've heard about early fuel pump deaths on vehicles it makes prefect sense; because they were notorious for dying early, and most were and are on pre-'03 models. And it's mainly due to the incompatibility with ethanol fuel. By '03 they (the vehicles) were at least partially ready for it and it's widespread use.


Makes sense to me- even though mine was built in 9/02, it would still be (at least partially) okay with E10?

Just a quick aside- what would need to me added to make an '01 Suburban 1500 (5.3 V8) E85 compadible? Could it be done?


----------



## Mr.Markus

Got the plow on? 70MPH for 2.5 hrs.might be a coolant sensor, specially if it comes and goes. But I agree check the codes.


----------



## Mr.Markus

I *REALLY*need to stop reading these old posts. I hope you have this problem solved by now.


----------



## B&B

mkwl;964901 said:


> Makes sense to me- even though mine was built in 9/02, it would still be (at least partially) okay with E10?


 It's an '03 model year so it's E10 compatible regardless of the build date.



mkwl;964901 said:


> Just a quick aside- what would need to be added to make an '01 Suburban 1500 (5.3 V8) E85 compatible? Could it be done?


It can be done but not without major expense for it to work correctly. Have to change the fuel module assembly, fuel injectors, add the necessary wiring for the E85 sensor and change the PCM for one prepared for E85. Not worth it IMO.


----------



## dsimo

Cosmic Charlie and the rest of who's interested. Got a hold of a good scanner, crank relearn didn't help. Computer seeing misfires on cyl's 1,5,6,8. Swapped coils, wires and plugs on known good cyl's with those on bad and misfire detection didn't change. Even with other Tech's nobody could actually detect a misfire happening (the way the computer is detecting you would think the motor would be falling on it's face). Suspect PCM at this point. FYI, computer doesn't really start detecting many misfires until 2500 or so RPM, so that is why it doesn't set a blinking CEL until over 60 MPH.


----------



## B&B

dsimo;971541 said:


> Cosmic Charlie and the rest of who's interested. Got a hold of a good scanner, crank relearn didn't help. Computer seeing misfires on cyl's 1,5,6,8. Swapped coils, wires and plugs on known good cyl's with those on bad and misfire detection didn't change. Even with other Tech's nobody could actually detect a misfire happening (the way the computer is detecting you would think the motor would be falling on it's face). Suspect PCM at this point. FYI, computer doesn't really start detecting many misfires until 2500 or so RPM, so that is why it doesn't set a blinking CEL until over 60 MPH.


Don't waste time or money on a replacement PCM because it won't fix it.

With all you've done previously I'd suspect a poor engine ground (common cause of the PCM detecting "false" misfires) or lack of fuel supply with actual misfires. Quite possibly from restricted injectors.


----------



## dsimo

Have performed the bulletin about the bad PCM ground on the right cyl head. No change. Will try to flash PCM before replacing, but you could waste a lot of time and money chasing this issue. Obviously there are a number of trucks out there with this issue that no one can pinpoint a cure all. Some trucks it's a intake, bad PCM ground, bad coil, or even wires. On those trucks there is an actual miss going on. If your truck is not actually missing and the computer thinks it is, what do you think the issue is? Still have not seen a post online that would tell you the answer to that, but it's more common than it should be.


----------



## dsimo

Truck is fixed. You have to eliminate the obvious possibilities first. I took truck to the dealer and had the PCM reprogrammed (my truck would have never been fixed with out this, but some may not need). On road test I got a P0300 code (this code would never set before) and the check engine light would now start blinking over 2000 RPM just like before. I could still see misfires on 1,5,6,8 cyl's. Eliminated the fuel and ignition systems as problem area's (like I said before, I've never felt it miss even though the computer thinks it is). Performed a crank sensor relearn 4 times before it took. When it did take, all my issues went away. No more misfire data, no more blinking check engine light. Good luck to the rest of you!


----------



## DBecerra

Ok, considering the last post on here is dated 2010 here I am 6 years later. I read through all post and was hoping someone might have a straight forward pin point answer/solution to my situation.

2004 5.3L 1500 Z71

About 4-5 months ago I replaced the knock sensors and wiring harness plus the sparkplugs (AC Delco);

I did not listen to my mechanic who said I should replace the sparkplug wires also and kept on trucking;

About 2 weeks ago my truck was really slugish in power so I replaced the spark plug wires; problem persisted;

I then took it in to O'Rielly's to get the check engine codes;

Came back with MAF Sensor out of range; Oxygen Sensor running lean; and two codes dealing with my fuel pump sensors; Noting that I have owned my truck for 3 years and never had the fuel level gauge worked I ignored the two codes about the fuel pump sensors;

Took the MAF sensor out carefully, sprayed it with MAF sensor cleaner and reinstalled it; 

The check engine light turned off for about 1 mile and came back on; I then unplugged the positive and negative terminals and left truck sitting for about 1 hr;

Turned truck back on check engine light was off and truck ran fine for about 1 day until it began to act sluggish again on the highway or anytime I punched the pedal;

So I decided to replace the MAF sensor;

The check engine light turned off completely but when I accelerated or punched it on the highway it felt sluggish again and the check engine light began to flash and turn off;

Considering the MAF sensor did not repair the problem I reinstalled the old MAF sensor and took back the new one;

I am now back to square one with a check engine light on and buddies recommending that I clean the oxygen sensor from carbon build up, another says to check the fuel line pressure, and another says to take my chevy to a scrap yard.

If anyone suffered through similar problems and solved it please let me know! Thanks in advance.


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## boutch

DBecerra;2134452 said:


> Ok, considering the last post on here is dated 2010 here I am 6 years later. I read through all post and was hoping someone might have a straight forward pin point answer/solution to my situation.
> 
> 2004 5.3L 1500 Z71
> 
> About 4-5 months ago I replaced the knock sensors and wiring harness plus the sparkplugs (AC Delco);
> 
> I did not listen to my mechanic who said I should replace the sparkplug wires also and kept on trucking;
> 
> About 2 weeks ago my truck was really slugish in power so I replaced the spark plug wires; problem persisted;
> 
> I then took it in to O'Rielly's to get the check engine codes;
> 
> Came back with MAF Sensor out of range; Oxygen Sensor running lean; and two codes dealing with my fuel pump sensors; Noting that I have owned my truck for 3 years and never had the fuel level gauge worked I ignored the two codes about the fuel pump sensors;
> 
> Took the MAF sensor out carefully, sprayed it with MAF sensor cleaner and reinstalled it;
> 
> The check engine light turned off for about 1 mile and came back on; I then unplugged the positive and negative terminals and left truck sitting for about 1 hr;
> 
> Turned truck back on check engine light was off and truck ran fine for about 1 day until it began to act sluggish again on the highway or anytime I punched the pedal;
> 
> So I decided to replace the MAF sensor;
> 
> The check engine light turned off completely but when I accelerated or punched it on the highway it felt sluggish again and the check engine light began to flash and turn off;
> 
> Considering the MAF sensor did not repair the problem I reinstalled the old MAF sensor and took back the new one;
> 
> I am now back to square one with a check engine light on and buddies recommending that I clean the oxygen sensor from carbon build up, another says to check the fuel line pressure, and another says to take my chevy to a scrap yard.
> 
> If anyone suffered through similar problems and solved it please let me know! Thanks in advance.


What the millage on the truck. Ever replaced the fuel filter. Sound like it starving in fuel. Filter getting clug or bad pump. Could have a vaccum leak. Do you have the specific code number.


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## Whiffyspark

Take it to a show and have it diagnosed before you fire a parts cannon. Cleaning an oxygen sensor isn't going to do anything. I wouldnt ignore fuel codes either. GM is known for having fuel pumps crap out around 100k. 

They also eat the valvetrain especially with AFM 5.3. Very common

Could also be a vacuum leak. Fuel pressure issue. Any number of sensors. Truck has coils as well


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## DBecerra

Whiffyspark;2134490 said:


> Take it to a show and have it diagnosed before you fire a parts cannon. Cleaning an oxygen sensor isn't going to do anything. I wouldnt ignore fuel codes either. GM is known for having fuel pumps crap out around 100k.
> 
> They also eat the valvetrain especially with AFM 5.3. Very common
> 
> Could also be a vacuum leak. Fuel pressure issue. Any number of sensors. Truck has coils as well


Thanks for your response. I have now replaced the o2 sensor bank 1 sensor 1 we dont have that code any more the MAF read .750lbs/min at idle at 600rpms but when i stomp on it a random missfire comes up no lean codes in any banks, fuel trims look alright but truck is still sluggish and code reader pulled random misfire and MAF circuit out of range. My immediate reaction is i have clogged cats. What do you think.


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## Whiffyspark

You need a scanner that can graph the maf to eliminate that. As well as the throttle body. 

If you think the cats are clogged remove front two sensors and drive it. See what it feels like. 

I don't think it has anything to do with the cats bases on the information you've provided


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## DBecerra

DBecerra;2134516 said:


> Thanks for your response. I have now replaced the o2 sensor bank 1 sensor 1 we dont have that code any more the MAF read .750lbs/min at idle at 600rpms but when i stomp on it a random missfire comes up no lean codes in any banks, fuel trims look alright but truck is still sluggish and code reader pulled random misfire and MAF circuit out of range. My immediate reaction is i have clogged cats. What do you think.


Turns out i had a clogged catalytic converter on bank 1. Problem solved.


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## Whiffyspark

DBecerra;2135061 said:


> Turns out i had a clogged catalytic converter on bank 1. Problem solved.


Did you pull the sensor out and try it?


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## Randall Ave

A vacuum gauge should have been able to show that.


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## 518CHEVYMAN

Read up on this whole thread. I've delt with 3 chevys 4.8 and 5.3 misfire consitant after full tune ups plenum gaskets high test fuel with additives maf cleaning compression tests. I'm at a full loss, one dealer fixed a 5.3 by replacing a certain fuse, last things are fuel filter and injections with green gaskets.


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