Misfire round 5 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-28-2012, 08:01 PM   #1
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Default Misfire round 5

Ok so I started noticing a slight misfire the other day....I thought it might be the LIM gasket leaking and fowling the plugs...now I'm not sure. I took out all the plugs, did a light cleaning on them and it really misfired bad...thought I might have cracked a plug putting back in, so I went and bought new plugs for every cylinder....fixed the miss at idle, but under acceleration it'* bad still....the car now smells like it'* running richer than normal. I have condensation buildup on the front of the motor on top of the LIM. Would that be the gasket, or is my bad O2 sensor causing it to flood the cylinders and fowl the plugs? The plugs on the even cylinders(back of motor) looked fine, the front looked a little dirtier, but not to the point of a misfire, and they didn't smell of burnt coolant. What gives? I'm getting to the point that I might be trading the car in unless I can get the problems to stop happening....also, the car has the metal LIM gasket on it already, and only has 134k on the motor.
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Old 04-28-2012, 08:48 PM   #2
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How'* the coolant level?
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Old 04-28-2012, 08:57 PM   #3
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well, it'* staying right above the cold temp level, and then when heated it'* just under the hot temp level. so..
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Old 04-28-2012, 09:41 PM   #4
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How old are the plug wires? They might be arcing out under acceleration.
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Old 04-28-2012, 10:59 PM   #5
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they are less than 3 months old and they aren't arcing......
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Old 04-29-2012, 02:33 PM   #6
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If the car smells rich it tells me your issue is probably spark, not fuel, related. You are smelling unburned gas in the exhaust. Is the CEL flashing? Have you checked for codes? Important to find out if this is random misfire, or related to specific cylinders, so we can track the problem down.

Plugs and wires would have been my first guess, but you say they are new. Could be a coil, but you want to know which cylinder(*) are misfiring so you can switch the coils and see if the misfire moves with the coils.

You are on here a fair amount and seem to have fairly good car sense. You should invest $30 or $40 and get a code reader if you don't already have one.
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Old 04-29-2012, 03:55 PM   #7
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eh...the one I need to invest in costs $15K(and I don't think it'* really not enough spark cuz the car has run rich sense I got it)....the problem now is, the plugs don't even act like they are being over fueled, it'* like its not getting enough fuel (only missing in + boost)....Talked to gunner and we are thinking it'* fuel system and not spark (all plugs look identical and come out clean). He thought that maybe the o-rings on the front fuel rail are leaking, but there is not build up and we checked and it doesn't mist when you rev the engine and get it to miss.....so maybe we're talking fuel filter/fuel pump sense both are original to the car. I brought the car back to school to see if I can get it put on the scanner(after class sense I'm putting a motor back in my uncle'* dakota this week and only have 4 days left in the shop)....then after that we start replacing parts(hopefully just the filter).
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Old 04-29-2012, 05:14 PM   #8
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Fuel pressure (pump, filter, injectors) is always a suspect in misfires. The only reason I was leaning to spark was your description of it smelling "rich" which tells me there is unburned gas in the exhaust. Perhaps, however, the rich smell at idle has nothing to do with the misfire under power and the misfire could be fuel related. It all comes down to getting a scan so you can focus on the issue. Otherwise its all guessing.
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Old 04-29-2012, 11:35 PM   #9
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If you have a bad coil pack it will often misfire once you start making boost but run fine in lower RPMs.
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Old 04-29-2012, 11:41 PM   #10
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The only problem is, we put it on the scanner today, and it'* just showing O2 sensor bank 1 is bad which it has been sense I got the car.....I was reading a few tech articles and they said that is attributed to a vacuum leak (can't find one though). I am showing no codes for a misfire, but it is misfiring.
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