Misfire cyl 4, cant figure out why... - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 11-25-2007, 05:48 PM   #1
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Default Misfire cyl 4, cant figure out why...

Ive been having a cyl 4 misfire now since we got the car, 96 bonnie SE...it seems to happen all the time, just at idle, and it may get better as driving cause the car seems to have power...
anyhow,
I have checked the ignition system thoroughly, swapped coil packs, and replaced the module, full tune up with new wires and plugs double plats, as I was told thats what it came with stock..
the plug is definatly firing as its colored like it should, however when removing the old plug the entire electrode was gone...but my search continues...I checked fuel pressure was ok, swapped injectors to see if the misfire would change cyl, it did not..so the injector is ok, did a compression test the effected cylinder is a bit low maybe 15-20 psi lower then rest...but that couldnt cause a constant mis could it?
checked the vacuum and it was a steady 16 at cold idle and rose to 20 when warmed up a bit, actually it rose and stayed at 20 after about 30seconds and after i rev'd her a bit...
Am I missing something?? could the computer be faulty? any suggestions would be GREATLY appreciated, as my girlfriend needs this car to get her to work and back..i want it to be running properly...
Thank you!
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Old 11-25-2007, 05:52 PM   #2
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Try a cylinder leakdown test on the affected cylinder and see what you get. Possibly a burnt valve.
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Old 11-25-2007, 05:56 PM   #3
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I suppose the vacuum test isnt very accurate then??
Will get myself a leakdown tester then, probably a good idea to have one anyway...
Is it damaging to the engine to continue running as it is? Cause its getting cold outside and if i need to do some major work id rather have it in the garage, and I cant bring it in there till my cars out, which will be in about a month or so when i get the time to finish it up..
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Old 11-25-2007, 06:18 PM   #4
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How many miles currently?
How is your coolant level?
What does your exhaust smell like?

Going out on a limb...if its cyl 4 and not cyl 6, and this is an intake issue.. I am betting LIMs over UIM at this moment...so be sure to check your oil level and appearance...anything other than just regular dark oil...such as milkyness, you got issues.
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Old 11-25-2007, 06:26 PM   #5
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Quote:
Originally Posted by wjcollier07
How many miles currently?
How is your coolant level?
What does your exhaust smell like?

Going out on a limb...if its cyl 4 and not cyl 6, and this is an intake issue.. I am betting LIMs over UIM at this moment...so be sure to check your oil level and appearance...anything other than just regular dark oil...such as milkyness, you got issues.
I'm with John on the LIM gasket as the cause. My wifes Olds 98 did the same thing except it was always #3. I finally changed out the entire intake per the article in techinfo and haven't had a problem since.
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Old 11-25-2007, 06:33 PM   #6
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mine has a random cylinder 6 misfire as well. never feel it, but it shows up on the code reader. plugs, wires, injectors are all fine

i just ignore mine and hope it will go away
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Old 11-25-2007, 06:45 PM   #7
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its at 125k right now, and the UIC was replaced, i was told that and found the old one in the trunk...but id much rather dig into the intake then to that back cyl head...so ill check that out next weekend too..
the oil ist milky, the oil press is kinda low maybe. at right above red for idle and half way during cruise and accel...and there is no noticable coolant loss...havent sniffed the exhaust but there is no smoke signals coing out at least..

Does anyone make a UIC in aluminum? im sure its been asked like a thousand times already, so if yall ignore it i understand :P
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Old 11-25-2007, 08:34 PM   #8
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Quote:
Originally Posted by index420
...the oil press is kinda low maybe. at right above red for idle and half way during cruise and accel...and there is no noticable coolant loss...
The oil pressure being so lowis not a good sign; time to get a mechanical gauge on there and confirm yor oil pressure.

As for the 'no noticible coolant loss'; mark the overflow and check it in a few weeks. I always attributed the slight loss I was seeing to evaporation but I assume now that it was slowing being drawn into the combustion chamber and fouling the plug. Like clockwork, every two months I was replacing that one plug.
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Old 12-11-2007, 12:50 PM   #9
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my #4 is missfiring too but i found that my wire is open from the top of the fat part of the rubber at the spark plug and the main wire going back to the coldpack
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