What causes a misfire? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 05-17-2005, 12:17 AM   #1
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Default What causes a misfire?

^^just like the title says^^
anyone?
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Old 05-17-2005, 12:21 AM   #2
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Combustion occuring at a point not intended or not at all. Too hot, too cold, too much fuel, too little fuel, weak spark...
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Old 05-17-2005, 03:26 AM   #3
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Carboned up spark plug(*), dirty air filter, improper plug gap, I think even a clogged cat can cause it but im not sure how. Bottomline can be caused by several things.

OBD2'* are designed to detect bad emissions or a misfire. If you experience a misfire the service engine light will flash on and off to alert you of a misfire. Not sure of OBD1'* however.
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Old 05-17-2005, 07:14 AM   #4
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A problem or something wrong. Could be as small as bad gas, could be as big as a blown motor.
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Old 05-17-2005, 08:47 AM   #5
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Also caused by crossing plug wires, [on distributer'd cars] the cap/rotor worn/timing WAY off.

Interferance from radio waves and the like.

OBDI does NOT detect misfires, at least mine doesn't. MAYBE OBD1.5


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Old 05-17-2005, 08:51 AM   #6
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Quote:
Originally Posted by opensourceguy
Interferance from radio waves and the like.

OBDI does NOT detect misfires, at least mine doesn't. MAYBE OBD1.5
Radio waves? No.

OBD1.5 (94/95) PCM'* do detect misfires.

9 times out of 10, it'* a wire or plug. With the wires, it'* either an open, or a short arcing to ground. Both will foul the plug.

Occasionally, it'* a coil., rarely an ICM, as the ICM would take out all 6 generally.
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Old 05-17-2005, 11:55 AM   #7
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Hook up a scantool and watch the cylinder missfire data.... You will know if you have a dead on miss...

Yes the 94-95 Bonnies do display Misfire data

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Old 05-17-2005, 01:42 PM   #8
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I think i mave a small misfire at idle. it goes away when i accelerate but i do have KR. I have new wires and the plugs are fairly new. I'll get some scan tool data within a week or so.
I'm still leaking a little oil from my headgaskets though so ultimatley that could be the problem. I'm still planning on replacing the MLS gaskets with regular felpro'* this summer but i have to save up some $ cause i'm doing more stuff while i'm in there.
Anyways
thanks guys, i'll keep ya posted.
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