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Rough idle and stumbles upon accelaration


George2002's Avatar
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09-18-03, 07:08 AM   #1  
Rough idle and stumbles upon accelaration

My wife just called and complained that the 1988 Pontiac Grand Prix 2.8 died at the light, restarted, but now stumbles upon accelaration and has a rough idle.

I was thinking either one of the coils went bad or one of the injectors.

Whats the best way to determine if its a coil or an injector?? Any other ideas as far as most likely causes on these cars?? Thanks!!

 
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09-18-03, 07:11 AM   #2  
Joe_F
See my The Basics.

 
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09-18-03, 10:15 AM   #3  
I had an '83 Cavalier and '92 Corsica that while driving would start to act funny and then just die. Wouldn't restart right away but if you let it cool they would restart. Had the catalitic converter unhooked and the problem went away. Probably not the best solution but at least I could drive the cars. The mechanic said it was a well known issue. Seems GM would have fixed the problem in 9 years time. (I think my brother's '87 Blazer had the same problem.)

 
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09-18-03, 11:10 AM   #4  
Joe_F
Had the catalitic converter unhooked and the problem went away. Probably not the best solution---

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Not the best, and in fact an illegal solution because if the shop is caught doing that it's a $10,000 fine. Also the car may not pass inspection if the converter is missing or disabled.

 
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09-18-03, 09:36 PM   #5  
Well, it looks like I have no spark from 1 of the coils. I removed it and measured the resistance on the primary and secondary but it was fine according to spec. I swapped this coil with the coil next to it that did work and it looks like the suspect coil works when placed in the other position. (Of course the good coil did not work when placed in the position of the original suspect coil. )

This means that the coil is fine and the module itself is bad for those two cylinders. Has anyone seen the module go partially bad like this?? I thought it would just go out completely.

Any tips as to what I am missing here? Next step is to remove the module and have it tested. Any tips for removal of the module?? Thanks, guys!!

 
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09-19-03, 05:47 AM   #6  
Joe_F
You have the right idea. Have the module tested.

 
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09-19-03, 07:24 AM   #7  
yes i have seen modules fail this way. If you swapped coils and still have no spark at that same cylinder, chances are good the module is failed. This is assuming the plug wires are okay. Once the module is off the engine, there is no 'tester' for it. The best tester for this module is the vehicle itself. Also you need to be testing for spark at each cylinder, using an st-125 or equivalent, found at any major tool dealer, Mac, Snap-on. They are not expensive. Unplug one wire at a time, attach the st-125, start the car and there should be good steady spark..

 
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09-22-03, 05:49 AM   #8  
Well, the problem with that car was the ignition control module.

I had it tested at 2 different Auto Zones where it passed. I felt pretty confident it was the module so I took it to a Pep Boys where they had a different type of module tester there.... the first time it passed but on retest, as the module got warm from operation it failed.

Just wanted to let everyone know.... and thank for your help, guys.

 
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09-22-03, 06:57 AM   #9  
Joe_F
Good for you. Good job.

 
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