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

Discussion in 'Chevy Trucks' started by Plowinpro03, Feb 28, 2009.

  1. Plowinpro03

    Plowinpro03 Senior Member
    Messages: 151

    .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
  2. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    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..
  3. Plowinpro03

    Plowinpro03 Senior Member
    Messages: 151

    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......
  4. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    MAF isn't the issue...

    Did you do the recent tune up as an effort to fix this issue?
  5. Plowinpro03

    Plowinpro03 Senior Member
    Messages: 151

    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....
  6. welj31

    welj31 Member
    Messages: 58

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

    Mebes Senior Member
    Messages: 386

    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
  8. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Did you notice an (or any) improvement right after you changed the cap? Even briefly?
  9. Plowinpro03

    Plowinpro03 Senior Member
    Messages: 151

    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?
  10. CityGuy

    CityGuy PlowSite Fanatic
    Messages: 16,904

    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.
  11. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    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".
  12. BigDave12768

    BigDave12768 PlowSite.com Addict
    Messages: 1,446

    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
  13. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

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

    ServiceOnSite Senior Member
    Messages: 928

    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
  15. goose311

    goose311 Junior Member
    Messages: 7

    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
  16. 70monte

    70monte Senior Member
    Messages: 468

    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.

  17. 70monte

    70monte Senior Member
    Messages: 468

    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.

  18. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    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. :rolleyes: Once they go to true coil on plug I look for them to once again open up the gaps.
  19. B&B

    B&B PlowSite Fanatic
    Messages: 12,777

    Open the vent up and close the plug gaps up. That'll fix it..it always does.
  20. 70monte

    70monte Senior Member
    Messages: 468

    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.