Shudder / Misfire around 55 mph and accelerating - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-31-2004, 12:14 AM   #1
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Default Shudder / Misfire around 55 mph and accelerating

Well, here'* my current problem that I'm trying to track down. It started with a misfire during rainy weather. I replaced the remaining two coils on the engine as a preventative measure, since I had replaced the first one and had similar symptoms. It worked fine for a few days, then today it came back. First it started while I was crusing at around 60 and then accelerated. When I pressed the gas down started shuddering. Then eventually it started misfiring at all rpms. So I took the car home and replaced the Bosch wires and AC Delco plugs with all AC Delco parts. Engine ran great until I got up to around 55, crusing with the TCC locked up, and then pressed the gas down without unlocking the TCC. Shudder again, with the boost gauge right around zero. It shudders until the TCC unlocks, then it'* not as noticable.

Any ideas? I'll see if the Catalytic converter has rattles in it tomorrow.
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Old 03-31-2004, 01:07 AM   #2
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I had a simular problem, and it ended up being the wires. You can test to see if you have a spark on all the coils. I'm gussing you do since it doesn't seem to misfire when not under much load. Does it stumble is you launch from a start? Just don't test it the way i did and get you fingers to close to the firing coil. It hurts a little.
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Old 03-31-2004, 02:02 AM   #3
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If it'* that noticeable, I'd say coil. 2 cylinder misfire. If it'* subtle, I'm betting wire.
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Old 03-31-2004, 09:02 AM   #4
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No stumbling from a 0-50 mph start... Just after the TCC locks up. I know we've seen this problem many times.

Today I'll try switching the first coil I replaced out with an old one.
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Old 03-31-2004, 09:23 AM   #5
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Thats what it was like for me when the wire went bad, when the boost got to zero the car would shudder. New wires and plugs and the problem has gone away.
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Old 03-31-2004, 11:47 AM   #6
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I switched the first new coil with one of my old ones before I drove to work today and no problems.

So we either have a bad new coil or an intermittent problem.

I will try putting the suspect coil back on today to see if it comes back. Don't forget, I just put on new wires and plugs last night. Took me about 1.5 hours to do. Then when I took it for a drive the miss was still there, but only under load.
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Old 04-01-2004, 02:51 PM   #7
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No problems yet... Just thinking about the way high moisture/rainy days could affect the ignition system. Which part of the system would be the most susceptable to moisture? The ignition control module?

What I still need to do is to try putting the suspect coil back on the ICM again to see if it misses. I will do that when I have time.
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Old 04-01-2004, 03:06 PM   #8
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Fuddy, pull your ICM and clean the bottom surface of it, and the top surface of the bracket. It may be fighting for a chassis/shield ground?
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Old 04-01-2004, 03:13 PM   #9
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Did you measure the resistance of the suspect coil? Compare that with another?
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Old 04-01-2004, 10:48 PM   #10
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Original coil - Top terminals - 6000k, bottom terminals - 1
Suspect coil - Top terminals - 8000k, bottom terminals - 1

Sounds normal... I wonder what'* going on here. I guess I'll have to clean the ICM next. I still would like to try putting the suspect coil back on.

I may be forced to take the fuel injectors off and have them professionally cleaned.
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