Misfire under boost - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 12-17-2005, 05:28 PM   #1
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Default Misfire under boost

My car has a problem where it misfires under boost. Sometimes it even misfires just as the motor is just leaving vaccum. But for the most part most of the misfiring happens alittle higher in the rpm range. I know something is wrong ( ie. injectors or coils ) and finaling today my CEL came on so I stoped by Autozone for the free scan ( P0304 I think it was ). It'* cyclinder #4 misfiring. My question is what is the more likly canidate to replace first injectors or coils? I'm leaning towars injectors becasue of the extra gas needed while under boost. But any comments, tips, opinions reguarding this would be welcomed.

Ed
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Old 12-17-2005, 05:32 PM   #2
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Check the plugs and wires. I would lean towards the plugs.
Unlikely a coil or injectors, would see other symptoms besides just boost condition. ie running lean, poor idle etc.
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Old 12-17-2005, 05:38 PM   #3
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My plugs were replaced about 2k ago and my wires are new as of July so I don't know if would really be that. And also months ago I had a very rare misfire and I took out my platinum 104 ( the only 104s the parts store had when I bought them) and put in copper cored 104s. But the misfire has continued and now has gotten worse but it still only happens under boost.
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Old 12-17-2005, 05:52 PM   #4
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Check your plugs and wires. That #4 is fouled now anyway. Measure the resistance of all the plug wires, and look for carbon scoring where the #4 may be arcing through the insulator to ground. This is easy to do at night at idle in the dark. Mist some water over the engine while it'* running and look for arcs.

You don't have an injector problem, and a coil would take out 2 cylinders.

Moving to 92-99.
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Old 12-17-2005, 06:56 PM   #5
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ive got the same problem actually, and ive got relatively new plugs and wires as well
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Old 12-17-2005, 07:12 PM   #6
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I just went outside and pulled the plug and it looked fine. (got pics if anyone wants to see for them self. ) I think I'm going to grab a spray bottle and look for arcing.
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Old 12-17-2005, 07:23 PM   #7
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Quote:
Originally Posted by NERV
ive got the same problem actually, and ive got relatively new plugs and wires as well
Relatively new plugs and wires have bitten many the member in the arse.

Even NEW wires have. Countless times. Plug wires are fragile.
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Old 12-17-2005, 07:35 PM   #8
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Just trired the spray bottle with a very fine mist..... I didn't see anything. So when I get one of my paychecks this week I think I'll get some new plugs. But if that doesn't work I'll have to wait 2 weeks for another check to start buying what I might need since this weeks pay from both jobs is already spoken for ( Christmas gifts ). Now I had my batt unhooked for alittle while and my CEL didn't go off do I need to have that one cleared out of the computer for it to dissapper or did I just not have the batt unhooked long enough? Time for a little test drive and see if she is still acting up
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Old 12-17-2005, 07:38 PM   #9
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Don't buy anything. You already said the plug looked fine.

Use a meter to check the end-to-end resistance of the wires.
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Old 12-17-2005, 07:39 PM   #10
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as for me i bet i actually do have a fouled plug, i accidnetally knocked a vaccum line loose recently and the car was misfiring during that, probly foule dit during that time
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