# 95 Silverado--Sluggish



## Joe123 (Jul 14, 2003)

I need some help. A couple of weeks ago I towed my boat to Opello, AR for a fishing trip on the AR River. Well, along the way, I began to notice that my truck was very sluggish and would sputter if the accelerator was punched quickly. It may even go dead if pushed quickly and hard enough. I got 10 mpg for the trip and I thought that wasn't so bad since I was towing the boat and didn't use overdrive. However, the next tank of gas I only got 10 mpg under regular driving conditions. I had been getting 12-13 or better. Up to 18 on the highway. I decided to change the spark plugs, fuel filter, air filter, and added high octane fuel and fuel system cleaner. That didn't seem to help. I finally took it to the shop and had them run a diagnostic test. They said the coil was bad and that I should not have used the type of plugs that I had used. I replaced the coil and replaced the plugs. It seems to run better but still isn't right. It still is sluggish when the gas pedal is mashed hard and especially when it is moving around 20-30 mph and then the pedal is pushed hard. The mechanic told me that I may need to replace the distributor cap and rotor button? I haven't done that yet. Does anyone have any suggestions as to what else I can do to make my truck run better? It is a 5.7 liter, 350 cid, less than 90k miles on it. It should burn the tires off the thing when the pedal is floored. Any ideas?


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## snowjoker (Feb 6, 2003)

Maybe it is the timing? or maybe the computer is going bad.Or possibly the fuel pump. BTW welcome to Plowsite :waving: dont worry there will be an answer soon enuff!!


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## wyldman (Jan 18, 2001)

The distributor cap and rotor may be the cause,but you should be able to visually inspect them for signs or arcing or excessive wear.

Does the engine just seem to lack power overall,or does it start to miss and sputter,as if your losing a cylinder(s) ?

A bad fuel pump,or plugged fuel filter would cause it.It could also be a plugged cat,or exhaust,timing chain worn,etc,etc.

I'd do the cap and rotor,and clean the throttle body out.See if it's nay better.If not,my next step would be to check fuel pressure,and verify the pump\filter are OK.

Post your findings.

Oh,and Welcome to Plowsite :waving:


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## Joe123 (Jul 14, 2003)

Thanks for the welcome!

My truck seems to run better when cold. It seems to go like it's supposed to when I first crank up. After it warms up, it seems sluggish at all times. It is worse when the air conditioner is running. 

I'm not very mechanically inclined but have some common sense. I have to ask....how would the timing be off if there wasn't any work done to it before it started acting up? Also, isn't 89K miles kind of early for a timing belt/chain to be worn to the point of problems? 

How would I go about checking fuel pressure? I have changed the fuel filter but not the fuel pump. 

I'm going to replace the cap and rotor today or tomorrow and I'll let y'all know where we are then. 

Thank you for your replies. Hopefully I'll get her running right soon.


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## Arc Burn (Oct 21, 2002)

Your cap and rotor could have loosened a hair and that could alter your timing,Chains have also been known to stretch although i'm not sure to the point it would effect timing How bout it there Wyldman?


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## wyldman (Jan 18, 2001)

The timing chain can loosen up,which retards both cam timing and ignition timing,and kills bottom end power.I wouldn't worry to much about that yet,go through the other basic stuff first.The distributor cap design on those trucks will not really rotate enough to effect timing if the bolts loosen up.When replace the cap,use a good quality unit,preferably OEM GM.Cheap caps will come back to haunt you later.

Has anyone ever done any engine work,distributor work,or maybe an intake gasket on this truck ? They may have not set the timing correctly afterwards.You can also check to see if the distributor has come loose,by trying to turn it by hand.Either way,check your timing.Should be 0 degrees,at idle in field service mode,or with the timing connector unplugged.

You can also check the advance system when check the timing.Timing should increase as the engine is revved up.It's possible you could have a bad knock sensor or EST module which could be retarding timing causing the lack of power.Any engine noise,or exhaust rattles can cause the problem too.The knock sensor assumes the engine is pinging,and retards timing.

To check fuel pressure,you need a fuel pressure gauge and the correct adapters.You can check it at either the back of the TBI unit,or at the fuel filter.It may be better to have a qualified shop check this for you.Have them install the gauge cold,and then monitor pressure as it warms up,to see if the pressure drops off under load.Spec is 9-13 PSI.

If taking it in to a qualified shop,have them throw the scanner onit,to check fuel trims,the O2 sensor,and watch the timing.They should be able to see what the problem could be.


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## Got Grass? (Feb 18, 2001)

Check the Cat converter while your at it. Exhaust not being able to leave the engine would cause a power loss by the built up pressure. My old 84' Cherokee used to be extremely sluggish especially at higher altitudes & act as if it was going to stall on me... 
Took it to the shop replaced the cat (not cheep) & the thing ran great till I sold it because my foot fell through the floor it was so rusted. It was real easy to tell the power difference before/after as the thing only had a small 4 banger that could hardly move the thing.


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## John DiMartino (Jan 22, 2000)

Joe, definetely check the cat convertor. My 350 is a 91,and its no barn burner either. The 95 350 was one of the slowest out there,they use a real small Y pipe and are only 200HP. Dont expect tire burning performance out of it. Mine is much snappier when its cold too,as the intake/engine bay warms up,power drops as air temps increase,this is totally normal.The 96 and newer Vortec 350 has 50+hp more than the 95,they do have much more problems than the TBI's though.


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## Joe123 (Jul 14, 2003)

Again, thank you for the help. 

I don't think anyone has done any work to the engine such as gaskets and such. I've only had this truck about a year and it was running MUCH better than this when I bought it. For that reason, I don't think timing is off unless it is through normal wear. One of y'all replied that timing should not be affected by normal wear/loosening of the bolts/etc.....?

I don't know what a knock sensor is or where it is located so I'd need some help with that one. The same goes for the EST module. (I feel like a dummy )

I took it to the shop and had a scanner run on it and the results were: bad ignition coil. I AM going to replace the cap and ball today and see where that gets me. Who should I take it to for checking the cat convertor? Any idea how much it might cost to replace it on this year model truck?


Keep the ideas coming....I really appreciate it!


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## wyldman (Jan 18, 2001)

If it hasn't been touched since the problem occured,and the distributor seems tight,then it's probably not timing.Check it,or have it checked if you take it back in.0 degrees BTDC.If you want a little more throttle response,and don't have e-tests where you are,you can bump the timing up to 10-12 degrees BTDC.It will wake it up a bit.

Knock sensor is on pass side of block,above pan rail beside the starter.It has a single wire,green in color.

EST Module is mounted on a bracket above pass side rocker cover.

Don't replace either until they have been checked.They were only suggestions.

It sounds like when you had it checked,they did a scope check,and not necessarily a electronic engine control test.With the proper scanner attached,you can read all (or most) of the data that comes into,and goes out of the ECM (computer).You can see if the knock sensor is working correctly or not.They should have plugged into a small black connector under the dash,with a little handheld scanner.

There are several way to check the convertor.

1)use a vacuum guage,and look for low vacuum readings.If the air can't get out,it can't get in,hence the low vacuum.

2)drill a small hole in the exhaust,upstream of the cat,and measure the backpressure.If the backpressure is excessive,the cat is plugged.

3)drop the y-pipe from the manifold,and take it for a test drive.If the power increases,then you have a plugged exhaust.

Any good diagnostic shop should be able to perform the above tests.Ask around,and find a good trustworthy shop.If you don't mind the drive,I'll look at it for you,no charge.Just bring me a coffee,double double 

Good luck,and post your findings.


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## wyldman (Jan 18, 2001)

Here's a few pics from the GM manual


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## wyldman (Jan 18, 2001)

Forgot the pic

EST module


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## wyldman (Jan 18, 2001)

Knock sensor


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## Arc Burn (Oct 21, 2002)

Thats it,I'm movin to Ontario,this damn guy's to good,i'll open a doughnut shop right next to your garagepayup


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## wyldman (Jan 18, 2001)

LMAO Arc.You'd better have good coffee.

You could work for me on the side,welding and stuff.Maybe even drive a plow truck for me,if you don't mind driving a Dodge


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## Joe123 (Jul 14, 2003)

So, I should ask if the mechanic has an 'electronic engine control tester' rather than a 'scope tester'? I'm going to replace the cap and rotor this afternoon and see what gives.

I kinda doubt that I'm gonna drive to Ontario for the tests but thanks much for the offer. I may even have an extra strong coffee mailed to you!  I'll ask around and see who might be able to run some performance tests on her. Thanks for the diagrams as well. 

How would the exhaust system get clogged? OH...I did have the muffler and tail pipe replaced right after that trip to AR but that was also after I began noticing the slow responsiveness and overall loss in performance. Don't know if that makes any difference...?

Will post again tomorrow after the cap and rotor change.


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## Arc Burn (Oct 21, 2002)

The packing in the catalytic converter can break apart,sometimes blocking the entire outlet pipe of the converter


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## Mike 97 SS (Aug 11, 2002)

It does sound very possible that the converter could be stuffed up, because you say it loses power when it gets hot. What Chris said to do about dropping the y-pipe is a great way to test to see if its a exhaust blockage problem or not. Another thing, no need to drill any holes in the exhaust to test if you dont wanna bother dropping the y-pipe, just unscrew the oxygen sensor and let that act as the hole. It is true though that every car doesnt feel as powerful when they get to operating temperature, which is why you see guys at the drag strip icing down their motors between races. But if you are saying you see a HUGE difference, then yea there is a problem, but little change in power is normal. Also, having the ac on will draw some power away from the motor too, that is true on any car. Chris, what is an EST sensor and what does it do? Not sure I ever heard of that one before. Also, you can advance the timing that much, 10-12 degrees over on these 350s? Maybe I should advance mine a little, hehe, it is right on 0 last time I checked it. Oh Arc Burn, that is true, the packing in a converter can break up and cause blockage, but you would hear it rattling around in the exhaust very easily. Once it breaks, the noise it makes jingling around inside the converter or pipes is very annoying and very pronounced. Mike


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## wyldman (Jan 18, 2001)

Joe 123 - yes,you want an electronic engine control test,to check for codes,and look at the real time data.A scope test only checks mostly the secondary igniton system.When I mention a plugged exhaust,it's usually referring to the catalytic convertor,but sometimes if the convertor comes apart,or a baffle (or packing) in the muffler comes apart,it can plug the muffler or the rest of the exhaust.

You might also want to check what type of convertor you have.If it's the really large fat pellet style,it's probably not the cat,as they very rarely plug up,as the exhaust just passes over the pellets,not through them.If you have the long narrow honeycomb style,then them are much more prone to clogging as the exhaust must flow through it.

Mike - I find it easier to drill a small hole,and screw in a test fitting to check backpressure.Then you just use a plug to close the hole.Were talking like 1/8",so it's no biggie.I will sometimes even just tack it closed with the mig.

I'm not a big fan of pulling the O2 as sometimes they don't come out,break off,or strip out the threads,then your in big trouble.  

The EST module,or electronic spark timing module,is used to control timing advance.Sometimes they will ****** the timing badly,and the truck will lack power.We had a member here with a similar problem causing excessive ******.

You can go 20 degrees if you wish,as the knock sensor will pull the timing back upon detonation.If you go that far then performance starts to deteriorate,and gets spotty,depending on the amount of detonation.I usually set them at 10-12 BTDC with no problems.Try it,you like it


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## Mike 97 SS (Aug 11, 2002)

Chris, thanks for explaining to me what that sensor is called and what it does. How can you check it to make sure its doing its job? Any ways? My truck has a little hesitation first thing in the morning when its cold, right when I pull away from the house. I catch the stop sign, drive away from it the truck shifts into 2nd and it loses it for a split second, kind of like a flat spot, then it comes back and its fine for the rest of the day. I tuned it all up and also put in a Coolant Sensor for the hell of it, thinking its not getting the right air fuel ratio when cold, but still does the samething. Its not bad, just a little flat spot or dead spot when it shifts into second gear and you give it more gas to get going. Its weird. Mike


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## Joe123 (Jul 14, 2003)

Well, I replaced the cap and button and noticed a good bit of difference. I didn't run the engine long enough for it to get really warmed up as I only drove a couple of miles taking the family out to eat. I'll find out tomorrow morning on the way to work. I noticed though that I still have the problem of a stutter or popping and almost engine kill when I'm moving about 15-25 mph and floor it. That ain't right.........

I didn't mention before that I have a 'sweet spot'......somewhere between 55 and 65 mph when under heavy acceleration (if you can call it that) the engine runs just as smooth and 'sweet' as I think it did before I began having the problems I am having now. Until it hit 55, it seemed like I was dragging a heavy weight, then, between 55 and about 70, the speedometer jumped and the engine ran like a top. Then, it would hit overdrive and the lugging would start again. 

I guess I'll decide whether I can live with what I've got tomorrow. I called the Chevy dealership this afternoon and they can run the electronic test for $65. I may just let them do it but will probably have to wait until next payday (next Friday). 

One more thing...I've noticed that my brake lights aren't working. The hazard lights work, the running lights work, and the signals work. Just no brake lights. The guy at the parts place told me that I probably have a broken wire somewhere. He said check the brake switch on the pedal. I looked for it briefly but didn't see it. I'll look again tomorrow. Is there a separate fuse for brake lights and hazard lights? The same filaments burn for both signals so I know it's not the bulbs.....?

Anyone want to buy a 95 Silverado really cheap? LOL
I just get aggravated when I can't figure something out. I'm not much of a mechanic but I'll try anything if I feel like I have enough info to go on. Thanks for your help guys. I'll keep you posted as to what I do next. I'm open to suggestions!


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## wyldman (Jan 18, 2001)

It is a hard module to diagnose.The best way is to swap it with a known good one from another truck.They are used on most GM truck V6's and V8's,so I'm sure you can find one to borrow somewhere.

Have you tried cleaning the throttle body and IAC ? Get a product called Ford Tune up Cleaner.Get the truck stinking hot,and spray the whole can down the throttle body and IAC passage.Give it just enough throttle to keep it from stalling while you do it.As the can runs out,let it stall,or turn it off and just let it sit for a 1/2 hour or so.Then fire it up,and beat the snot out of it for a good long drive.It should help your problem.

Removing the battery cable,and doing a relearn afterwards is also a good idea,as it will run better.

One other thing to check is maybe a leaking TBI base plate gasket.


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## Mike 97 SS (Aug 11, 2002)

Yea Chris, I did clean out the throttle body. I didnt actually take out the IAC and clean it though, the truck idles absolutely perfect, cant feel it idle, so I figured maybe the IAC is good. Also, this truck has only had premium fuel since new, 93 octane, never ever saw regular or middle grade. I know Fords have alot of problems with the IAC, but I dont think the Gm's do, do they? Its a hard problem to try and fix because it is only first thing in the morning when I pull away from that stop sign and go. After that its good the rest of the day so I cant even reproduce it, I have to wait until the next day, haha. Thats why I checked the timing too and it was at 0. I should raise her up a bit though, hehe, a little extra power wouldnt hurt even if it didnt cure the condition. Mike


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## wyldman (Jan 18, 2001)

Mike - try the Ford cleaner like I suggested.It also cleans and decarbonizes the intakes,valves and combustion chamber.It will make a noticeable difference.

GM IAC's like to get dirty and stick,hence the need for constant cleaning.I'll disagree the Ford's have a lot of IAC (or Air Bypass valve in Ford terms) problems because they don't.It is usually just misdiagnosed.The Ford's use the ABP valve a lot more to control idle,and if something else is off,they can't keep up.I spent 8 years at Ford as the head tune-up\electronics guy and one ever saw 2 that were actually bad.A lot of it to is Ford's $hitty programming that can't keep up either.

You may also want to look at your O2.I assume you have a scan tool at the shop ? Watch the O2,and make sure it fluctuates rapidly from lean to rich.It should swing continuously when in closed loop.Some scan tools will also read 02 crosscounts.They should be high,and stay high,usually around 6-8.The reason I mentioned this,is the O2 directly affects block learn and integrator values.These values are stored to calculate the fuel map.When hot,and in closed loop,the ECM makes minute adjustments to the air\fuel ratio to keep it as close to stoichiometric as possible.When cold,or in open loop,it relies on fuel trims stored in the fuel map.So if your O2 is incorrect,the fuel map is incorrect,and you will have a cold intermittent stumble.

Check your PCV valve too,as a lot of aftermarket (usually Fram's) PCV's have too much flow,too early off idle,which will cause a lean stumble,that may be more noticeable cold.


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## wyldman (Jan 18, 2001)

Joe 123 - Some GM trucks were bad for brake light switches burning out.The switch is WAYYYYY up there at the top of the brake pedal.It has a little plastic clip that hooks around the pedal arm.You may actually have to remove it to test it.

Have the dealer not only check for codes,but to spend some time (ie road test) to look at the data stream.Have them check fuel pressure and timing too.

How's the ignition wires ? When you say the engine sputters and pops,that sounds like a secondary ignition problem.Maybe the wires are bad ? Spray them down with water (especially around the back of the heads),and if your problem gets real bad,then it's the wires.You can also peek under the hood in the dark (after you wet the wires down,and watch for arcing.

The lack of power still sounds like maybe a fuel pump,timing or plugged cat.

Good luck and keep us posted


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## Mike 97 SS (Aug 11, 2002)

Chris, thanks alot for that whole write up. The oxygen sensor is new and so is the PCV valve. We dont have a scanner at the shop, we arent that up to the times yet.  I will try to get that Ford cleaner though like you said. Thanks again for your input.  Mike


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## whwright (Jul 16, 2003)

Hey Wyldman, is the "Ford Tune-up Cleaner" similar to GM's "Top Engine Cleaner?"


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## wyldman (Jan 18, 2001)

It's similar,but not quite the same.Same type of product,and intended use.I find the Ford stuff just works better.


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## Joe123 (Jul 14, 2003)

I'll check the wires this weekend. I may even replace them..just for the heck of it. Thanks for all of the advice. I'll post as I do different things and until I get it right.


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## Joe123 (Jul 14, 2003)

OK....I replaced the brake light switch and the brake lights still don't work. I checked and replaced the fuse (it wasn't blown). 

I'm going to see a friend who is a mechanic this afternoon who said he could check my fuel pressure and I'll get him to check my timing. Is there anything else I should get him to check? He said he doesn't have a diagnostic computer but he'd check what he could. He told me that if the Cat convertor was stopped up the exhaust would be making a swishing sound...like air coming out of an air hose??? I haven't listened that close. Hopefully he'll be able to get my mean green machine purring again. I'll let y'all know how it turns out.

BTW, payment will be a bottle of his favorite beverage. That's pretty cheap for a good mechanic!!


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