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  1. #1
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    Car mechanical question-GM coil packs

    I have no ideal how these work. Got a 98 with 4 coil packs. was getting CE light. Checked code and it was a misfire in cyl. 4. Sure enough no fire to cyl. 4. Went to buy a coil pack at the auto parts store. Guy asks whats happening, I tell him and he says I should have 2 dead cylinders. He says the whole coil goes bad not just one side. I didn't think I had 2 dead cyl.s so when I get home I pull the other wire and there is spark. Replace coil and all of a sudden no fire either post. Made in China so maybe I got a bad coil. Put old one back on and no fire either post. What did I do? Put volt meter to the contacts that the coil connects to and one post read 13.8v and the other was .126v. It appeared steady so what tells the coil when to fire. No other wires connect so I figured the voltage would cycle.


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    To add. I see that the whole "tray" that the coil packs sit on is the ignition control module. It's also a $250 part. Guess that could cause my problem and it's time for a trip to the junk yard.

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    You guys are as clueless as I am I guess. Just found out that you have to complete the circuit on these for both cylinders to fire. I think the whole time I had no spark on the 1 cylinder the 4 cyl was not plugged in. Make sense?

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    I'm a drivetrain tech, but I work on other things once in a while for a change of pace.

    Your miss fire code could be caused by fuel, compression, or ignition. Did you try to swap coils with one of the other cyls? What about the wire? Does it feel like it's miss-firing? Or is this a random code? Did you clear the code and see if it came back? Does you scan tool have a miss-fire counter? What yr, make, and model?

  5. #5
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    Quote Originally Posted by CrazyCooter View Post
    I'm a drivetrain tech, but I work on other things once in a while for a change of pace.

    Your miss fire code could be caused by fuel, compression, or ignition. Did you try to swap coils with one of the other cyls? What about the wire? Does it feel like it's miss-firing? Or is this a random code? Did you clear the code and see if it came back? Does you scan tool have a miss-fire counter? What yr, make, and model?
    I'm pretty sure it would be misfiring if there was no spark, but yes it has had a miss for a while now. Code has been cleared twice and came back. Not sure how make or model would make a difference. Lets see about 10,000 misfires have occurred since I've drove the car 500 miles with this condition. (BTW, number was pulled out my ass)

  6. #6
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    Quote Originally Posted by NCHeel View Post
    I'm pretty sure it would be misfiring if there was no spark, but yes it has had a miss for a while now. Code has been cleared twice and came back. Not sure how make or model would make a difference. Lets see about 10,000 misfires have occurred since I've drove the car 500 miles with this condition. (BTW, number was pulled out my ass)
    Have it your way.

    Good luck figuring it out...

  7. #7

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    the year and model matter becuase gm has used different style coils on different models and years. if you look at a 3.4 or 3.1 engine the car uses a coil rack. if you look at a gm newer gm 6.0 or 6.2 engine each cylinder has its own coil they don't share.





    im going to guess you changed the plugs and wires already at least once? also if it s a gm 3.1/3.4/3.8 stay away from bosch products for some reason those engines don't like there plugs.

    if your set up on a rack and your only having an issue with one coil then its probably the ignition control module that sits right under the coils. the coils share all the same wiring up till that point i believe ( sorry its been a while since i looked at v6 coil rack). my guess would be if there isnt a problem with the coil its going to be in the module.

  8. #8
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    Quote Originally Posted by stingray152003 View Post
    the year and model matter becuase gm has used different style coils on different models and years. if you look at a 3.4 or 3.1 engine the car uses a coil rack. if you look at a gm newer gm 6.0 or 6.2 engine each cylinder has its own coil they don't share.





    im going to guess you changed the plugs and wires already at least once? also if it s a gm 3.1/3.4/3.8 stay away from bosch products for some reason those engines don't like there plugs.

    if your set up on a rack and your only having an issue with one coil then its probably the ignition control module that sits right under the coils. the coils share all the same wiring up till that point i believe ( sorry its been a while since i looked at v6 coil rack). my guess would be if there isnt a problem with the coil its going to be in the module.
    I see what your saying, but since I gave all the pertinent info, '98 with 4 coil packs and one coil pack for every 2 cylinders, then it is a V8 with a coil rack or what I was calling a tray.

    Now on to the symptoms, after researching I messed with it some more last night. The car still idles fairly steady but it seems that now the first 2 coil packs are not firing (7-6 and 1-4). Swapped the 7-6 coil pack to the 1-4 slot and nothing. It does get extremely hot. Way hotter than the rest. Put the new pack in the 7-6 slot and it seems that only the 6 cylinder has a weak spark. The other 2 coil packs, that I haven't touched, have plenty of spark and if you pull one of their wires the engine will immediately stumble. The car came with a engine protection system that was suppose to protect the engine in case it overheated by running on 4 cylinders and alternating the cylinders to keep the temps down and allowing you to drive the car up to an additional 50 miles. That's how it runs now, like a 4 cyl with zero power. I'm thinking that it is the control module but it stumps me as to why it gets worse every time I try to fix the problem.

  9. #9

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    Quote Originally Posted by NCHeel View Post
    I see what your saying, but since I gave all the pertinent info, '98 with 4 coil packs and one coil pack for every 2 cylinders, then it is a V8 with a coil rack or what I was calling a tray.

    Now on to the symptoms, after researching I messed with it some more last night. The car still idles fairly steady but it seems that now the first 2 coil packs are not firing (7-6 and 1-4). Swapped the 7-6 coil pack to the 1-4 slot and nothing. It does get extremely hot. Way hotter than the rest. Put the new pack in the 7-6 slot and it seems that only the 6 cylinder has a weak spark. The other 2 coil packs, that I haven't touched, have plenty of spark and if you pull one of their wires the engine will immediately stumble. The car came with a engine protection system that was suppose to protect the engine in case it overheated by running on 4 cylinders and alternating the cylinders to keep the temps down and allowing you to drive the car up to an additional 50 miles. That's how it runs now, like a 4 cyl with zero power. I'm thinking that it is the control module but it stumps me as to why it gets worse every time I try to fix the problem.
    just out of curiosity what kind of plugs are in the car? i know this maybe an odd question. but as i stated earlier i had a lot of problems with Bosch plugs in the past the car would run like crap.

    are you throwing any other codes then the misfire now?

    im sure the parts store would exchange the part if you believe there is a problem.

    i have gotten a lot of defective parts. just a few weeks ago i bought a new headlight for a car and put it in and it didnt work. for some reason i thought was a wiring problem and it turned out it was a bad brand new headlight.
    id bring it back and get a replacement if that doesn't work id go with the control module.

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