# Ignition issues when moist out...truck turns over, but a no go!?!?!?



## Plowinpro03 (Dec 18, 2007)

.It's a 96 tahoe, owned since new. It's now my plow truck. I can't for the life of me figure out WHY on wet/rainy very moist days (like today,,..primarily when all the snow melts, and there's LOTS of moister in the air).....it will never fire up, it turns over, and i get no go on all cylinders...it lumps....maybe 2 or 3 cylinders fire up.

Rotors,cap,plugs,wires all fairly new, coil IS BRAND NEW.........On any average day, it will start. 20 below no problem, 110 out, no problem, any were in between..no problem. It can sit for months, and it'll start...but when it's exceptionally moist out.....wont start...what the hell gives???


(I do take the air filter off thinking that my get to wet...yet it still wont start)

Maybe moister in the gas tank? See, it never matters when it's moist out, winter or summer..it'll do the same thing. Ill have to let it sit for a day or so b4 it starts now.........>>>.any thoughts?

Thanks in advance guys...wesport


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## B&B (Nov 4, 2006)

What brand of cap & rotor?
What brand of wires?
What did you set the plug gap to?

...it all matters on the '96-'98 Vortec trucks when it comes to starting in damp weather believe it or not..


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## Plowinpro03 (Dec 18, 2007)

B&B;762735 said:


> What brand of cap & rotor?
> What brand of wires?
> What did you set the plug gap to?
> 
> ...it all matters on the '96-'98 Vortec trucks when it comes to starting in damp weather believe it or not..


Well, the cap and rotor are BWD....the coil IS ACDelco..oem part, the wires are accel, and the plugs are auto lights gaped to factory settings.. ***I've been running the same for years***........

Im startin to lean more towards the maf...or maybe the plugs are bad...not sure......


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## B&B (Nov 4, 2006)

MAF isn't the issue...

Did you do the recent tune up as an effort to fix this issue?


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## Plowinpro03 (Dec 18, 2007)

B&B;762747 said:


> MAF isn't the issue...
> 
> Did you do the recent tune up as an effort to fix this issue?


Yes..haha... The issue was present b4. Im starting to think...what are the odds of it being the di-electrical grease in the plug wires. That gets really tacky, im wondering if it's absorbing moister some how and its break the connection in the plugs....


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## welj31 (Jan 20, 2009)

Try a very close inspection of your cap. You may find a hair line crack between terms.


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## Mebes (Feb 7, 2004)

In my experience moisture in the air problems are almost always plug wires.
How old are yours?
If this truck still wont start then open the hood open at night in the dark and have someone else crank the engine, and you will probably be able to see the sparks.

If the truck is running normal, because it has dried up then get a squirt bottle and spray the plug wires one at a time with water with the engine running.
When you hit the bad spot it will start to stumble or you may see sparks.

When checking cap for hairline cracks as welj31 suggested run your finger around the surfaces and look for Carbon.
Carbon is normal around the contacts but not in other areas.
Good luck
S


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## B&B (Nov 4, 2006)

Plowinpro03;762839 said:


> Yes..haha... The issue was present b4. Im starting to think...what are the odds of it being the di-electrical grease in the plug wires. That gets really tacky, im wondering if it's absorbing moister some how and its break the connection in the plugs....


Did you notice an (or any) improvement right after you changed the cap? Even briefly?


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## Plowinpro03 (Dec 18, 2007)

B&B;763411 said:


> Did you notice an (or any) improvement right after you changed the cap? Even briefly?


No, what i am going to do now tho is just replace everything with new, cap/rotor/plugs/wires, and go from there. Im going to make an assumption that if those aren't the case possibly ECU?


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## CityGuy (Dec 19, 2008)

Go back to ac delco plugs I have had nothing but problems in gm products with anything but acdelco plugs. Cap and rotor and wires don't seem to matter but the plugs always seem to be a problem. Just my opinion and expierence.


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## B&B (Nov 4, 2006)

Plowinpro03;763551 said:


> No, what i am going to do now tho is just replace everything with new, cap/rotor/plugs/wires, and go from there. Im going to make an assumption that if those aren't the case possibly ECU?


It's not a PCM issue...they seldom die and when they do they die completely.

1) Get a GENUINE GM cap & rotor on it. The aftermarket stuff is garbage.
2) Ditto with the Accel wires. It's a Tahoe not a race car. Either NAPA's premium wires or GM's own wires work best.

3) Get the Autolite (but don't) plugs out of it. Replace with A/C Delco's 41-932 plugs GAPED TO .040! DON'T gap them at .060 like what was once specified. GM sent out a TSB ages ago to close the gap up on these truck due to this very issue. It takes so much secondary power to jump a .060 gap that it prematurely wears out the secondary ignition components and coil....especially the cap and is one reason these caps burn through and cross fire.

And most important, check the vent hole in the bottom of the distributor housing for blockage. When the vent gets plugged up it traps any moisture in the distributor housing/cap...and will create the exact situation your finding yourself in. If the vent has a metal screen in it still.... knock it out with a screwdriver. Prevents the issue from reoccurring by allowing the distributor to "breath".


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## BigDave12768 (Nov 17, 2006)

B&B doesnt this sound like he just getting a vapor lock? My advice would be get a new fuel filter first. If truck is firing over and running fine but not moving. You are starving truck for fuel Put a pressure gauge on it. If it is wires. Chek it out side in the dark. You will see them arcing all over the place. 

The one other thing it maybe. Your computer maybe gone also. Find the computer and look at gel coating over the top. See how deep the cracks are. If the board is exposed it could be that. But I would go with a vaopr lock and change filter. Should be an inline one on Drivers side of motor. 2 16mm wrenchs to take off I think


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## B&B (Nov 4, 2006)

They don't vapor lock...especially when their cold.


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## ServiceOnSite (Nov 23, 2006)

i know im going to spell this wrong, replace your module in your distributor cap. its a 30 part and you can leave your wires still on the cap. If you have a small crack in it when its moist out it gets in and wont allow it to start. Just went through the same problem on my 92


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## goose311 (Jan 21, 2009)

get rid of the autolites chevy motors don't like them they are pretty much a ford plug put ac delco back in and it will run fine for some reason chevy motors only like the ac delco's or accel's will work also


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## 70monte (Feb 5, 2008)

B&B;763983 said:


> It's not a PCM issue...they seldom die and when they do they die completely.
> 
> 1) Get a GENUINE GM cap & rotor on it. The aftermarket stuff is garbage.
> 2) Ditto with the Accel wires. It's a Tahoe not a race car. Either NAPA's premium wires or GM's own wires work best.
> ...


B&B, does closing up the plug gap apply to the 7.4L as well as the 5.7L? A guy on another forum I go to, suggested putting the gap at .045 on both the 7.4L and 5.7L? I have an Alldata subscription for both of my trucks and I have never seen the TSB you are referring to. Do you have a link to this or the TSB #. I would like to read it. Thanks.

Wayne


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## 70monte (Feb 5, 2008)

I run pretty much all AC-Delco ignition stuff on both of my 98 trucks. My 7.4L still has an aftermarket cap & rotor on it that was on it when I bought it. They were new so I left them on. It already had replacement AC-Delco wires on it and I replaced the coil with an AC-Delco replacement. I replaced the Bosch +4 plugs that were in it and put in AC-Delco Rapidfire #12's in it. 

My 5.7L has all Delco ignition parts on it except for the wires which are Magnacor. I've had alot of ignition issues on this truck with the coil arcing to ground and the wires lighting up in different spots. I don't know what causes it but the replacement parts usually don't last long before this problem resurfaces. I will check the distributor vents to see if they are plugged up and causing problems.

Wayne


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## B&B (Nov 4, 2006)

70monte;764328 said:


> B&B, does closing up the plug gap apply to the 7.4L as well as the 5.7L? A guy on another forum I go to, suggested putting the gap at .045 on both the 7.4L and 5.7L? I have an Alldata subscription for both of my trucks and I have never seen the TSB you are referring to. Do you have a link to this or the TSB #. I would like to read it. Thanks.
> 
> Wayne


It works better on any application that originally called for a .060 gap regardless of engine or ignition. Smoother idle, less misfires, and longer ignition component life across the board. IIRC they never posted a "formal" TSB on it. It was sent out on the wire to dealers via GM's own Techlink...while at the same time making rolling revisions to the tune-up specs. If I can find a copy of the original bulletin I'll get it to you.

All the V8 light trucks from '96 to the '04 model year were originally spec'd for a .060 gap. But in '05 it was changed to .040 without any other changes to the ignition system or its design....due to these same reasons.

GM tried a .060 plug gap in the 70's and it didn't work, they tried again in the 80's and it didn't work, and once again in the late 90's/early 2000's and it still didn't work...so they're back to the smaller gap specs again.  Once they go to true coil on plug I look for them to once again open up the gaps.


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## B&B (Nov 4, 2006)

70monte;764335 said:


> My 5.7L has all Delco ignition parts on it except for the wires which are Magnacor. I've had alot of ignition issues on this truck with the coil arcing to ground and the wires lighting up in different spots. I don't know what causes it but the replacement parts usually don't last long before this problem resurfaces. I will check the distributor vents to see if they are plugged up and causing problems.
> 
> Wayne


Open the vent up and close the plug gaps up. That'll fix it..it always does.


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## 70monte (Feb 5, 2008)

B&B, thanks again for the information. I will pull the plugs on both trucks and adjust the gaps and check the dist. vents and open them up. I have had probably five sets of plugs, wires. coils and caps & rotors on the 5.7L because of the arcing problems and loss of power. I always knew when it started because the truck would feel very doggy and start pinging all of the time. Gas mileage would always go down. I would check the coil in the dark and it would be arcing from the coil body to the metal part that surrounds the coil. You could watch the arc jumping at idle. The plug wires would also be lighting up like a christmas tree. Luckily the current ignition parts are not doing this yet so hopefully this information will prevent it from ever happening again. Thanks again.

Wayne


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## 2COR517 (Oct 23, 2008)

B&B;763983 said:


> . Replace with A/C Delco's 41-932 plugs GAPED TO .040! DON'T gap them at .060 like what was once specified.


The parts guy just gave me 41-993. I checked another auto store, and they pulled the same number. This is also the part listed for my truck on acdelco.com.

Is there a big difference?

Going in my 97 2500 with Vortec 350.


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## B&B (Nov 4, 2006)

They're the same plugs. 

41-932 is the old p/n thats being phased out. 41-993 is the most current superseded p/n. Either one is fine.


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## 2COR517 (Oct 23, 2008)

B&B - As always, you are THE man.

Thanks for sharing your vast knowledge with us.


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## 70monte (Feb 5, 2008)

B&B;766169 said:


> They're the same plugs.
> 
> 41-932 is the old p/n thats being phased out. 41-993 is the most current superseded p/n. Either one is fine.


B&B, what is your opinion on the AC-Delco Rapidfires(the newer single platinum versions)? I'm running these because I was losing the little platinum discs off of some of my factory plugs in the 5.7L and didn't like that. I realize that the Rapidfires won't last as long but I never leave plugs in for 100,000 miles anyway. Both of my trucks seem to run fine with them.

Wayne


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## B&B (Nov 4, 2006)

The Rapidfire's are fine Wayne. If the truck works well with them there's no reason to swap them out as long as the gap is correct.


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## 2COR517 (Oct 23, 2008)

Genuine GM Wires are $126. Napa Premium are $80. Should I spend the extra $45?

Can the timing be adjusted for these trucks? If so, what is the procedure?


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## goose311 (Jan 21, 2009)

i'd spend the extra $45 and get the ac delco wires...i think you can still time it


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## 70monte (Feb 5, 2008)

B&B;766419 said:


> The Rapidfire's are fine Wayne. If the truck works well with them there's no reason to swap them out as long as the gap is correct.


Thanks B&B. I will regap the plugs in both trucks.

Wayne


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## B&B (Nov 4, 2006)

2COR517;766556 said:


> Genuine GM Wires are $126. Napa Premium are $80. Should I spend the extra $45?


 Either set of wires are fine. I commonly use both and have never found any reliability or performance differences between the two.



2COR517;766556 said:


> Can the timing be adjusted for these trucks? If so, what is the procedure?


Ignition timing is PCM controlled and not adjustable. You do set the phase angle via turning the distributor which watching the phase angle through a scanner, but your not changing the actual timing. Your just establishing reference for the PCM between the cam and crank sensors...nothing more.

If you rotate the distributor or disturb it on one of these '96-'99 Vortec trucks you need a scanner to re-set the correct phase angle so don't touch it in attempt to advace the timing...they're not an old school engine.


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## 2COR517 (Oct 23, 2008)

B&B - you confirmed my suspicions for both. My local GM dealer doesn't even stock the wires, they probably just use the Napa wires. They do stock the Delco Cap & Rotor, and they're actually cheaper than Napa. 

I won't be touching the distributor


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## 70monte (Feb 5, 2008)

I regapped the plugs in the 7.4L and did a couple of stupid things. I had a problem reinstalling one of the plugs because the heat shield was bent and in the way and ended up messing up the threads on the plug so off to the parts store for a replacement for that plug and for the cracked one I discovered. 

When I started the truck up it was running real bad and one of the wires was arcing to the heat shield. I ended up discovering that two of my plug wires were not on the plugs very well. Talk about a novice mistake. I've been working on cars for over 20 years and I do that. I just hope I didn't ruin those two wires and the cap and rotor. I'm going to drive it tomorrow and see how it runs.

Wayne


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## 2COR517 (Oct 23, 2008)

I pulled the Bosch +4 plugs Saturday. The gaps were easily .060. Put in the Delco plugs gapped at .040. UNBELIEVABLE difference. I'm not kidding. The truck couldn't get out of it's own way before. No power, pinging, sloppy idle. Runs great now, plenty of power. There's a healthy grade just before my house. Truck walked up over it no problem, and ran much cooler doing so. Going to replace the wires with the NAPA Belden Max this week, and probably put on a new Delco cap and rotor. Bought some split loom (in matching blue, of course) to protect and separate the wires where necessary. Wires, cap, and rotor are about a year old. But now everything, including air & fuel filters, will be all new with the same age. Can't what to see what I can get for mileage now.

Many many thanks to B&B for his extensive knowledge and advice.

Palmer


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## 70monte (Feb 5, 2008)

My 7.4L had the Bosch +4's in it when I got it and it had a terrible idle. I replaced these with Delco Rapidfires and it ran much better.

Wayne


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## B&B (Nov 4, 2006)

I generally don't like to trash a product but the Bosh +4's are worthless for these GM applications. So many times in the past guys install these plugs as an effort to take advantage of all of the manufactures advertised claims...but all they do is create drivability issues while lightening your wallet.

Use nothing but the generals recommended plugs in these truck period and you'll be happier.


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## fakemam (Mar 21, 2008)

*Aman!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!* B&B ive treid them all and always go back to the acdelco


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## 2COR517 (Oct 23, 2008)

So I took the truck for a decent road trip today. About 200 miles. Maybe 80 miles on the highway at 70 mph. That's taching 2,400 thanks to 4.10 gears so I don't go much faster. Some stop and go driving in the three "cities" we went to. The rest was rural roads with some moderate hills, between 40 and 55 mph. Truck was easily 7,500 lbs. Truck drove great. Plenty of power, smooth acceleration. Only downshifted a couple times, once again thanks to 4.10 gears.

The new plugs are in, and the air and fuel filter are new. Still have the Duralast wires and cap & rotor on. I know the wires are gone, truck ran like crap in the rain the other day. 

Anyway, pulled about 14 mpg. :redbounce Probably the best tank since I bought the truck. Gonna do the wires, cap & rotor this week. I don't know how much difference it will make in economy, but it will certainly run better in the rain.


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