1996 Bonne SE Cylinder 2 Misfire - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 08-23-2010, 05:55 PM   #1
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Default 1996 Bonne SE Cylinder 2 Misfire

My son'* Bonne SE started throwing a P0302 code last week so this past weekend I did the following:

1) Erased the code to see if it came back...it did.
2) Swapped the spark plug and plug wire and the misfire code remained on Cylinder 2.
3) Swapped the ignition coil, still Cylinder 2 misfire.
4) Swapped the fuel injector, still Cylinder 2 misfire.

Ran out of time so didn't have a chance to pull and/or check the ICM. Read on the forums here that it could also be the O2 sensor. Any way to test that without putting in a new one? How likely is it to be an O2 sensor or ICM when it so steadfastly sticks on just cylinder 2? If the voltage on all 3 coils is good...how likely is it to be the ICM? Should I just move on to something else...i.e., the valves?

There was a small black circle next to the electrode and appeared that there was some kind of carbon build-up on the plug...plugs were new in April when I installed a new LIM and UIM gasket after the LIM gasket failed and flooded the engine with coolant. It'* had other mechanical issues but the engine itself has been purring like a kitten up until it threw the code. The misfire itself isn't incredibly bad...there'* just a bit of extra "vibration" that doesn't belong there.

What are my next steps in sequence? Thanks!
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Old 08-24-2010, 07:35 AM   #2
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Compression test the cylinder. It'* unlikely the ICM, although it can happen.
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Old 08-24-2010, 09:22 AM   #3
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Don't see this being the O2 sensor either. It'* something unique to that cylinder. You can try swapping injectors. If after that you still have a misfire I say pull the valve cover and inspect the valve springs. A broken spring will not show up with a compression test, only a visual test will tell you for sure. I have seen this two times now. All tests come back good, check the springs and ta da, broken spring on the exhaust valve.
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Old 08-24-2010, 11:58 AM   #4
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I'm going to pull the valve cover when I get home from work tonight, but we had a couple items that might help a bit with diagnosis. First, when my son decelerated from about 40 mph and made a 90 degree right hand turn, the car stalled. It started right back up but now he'* paranoid since he completely lost power (steering, brakes, etc.) when it happened. We weren't able to duplicate the stall doing either left or right hand turns from similar speeds so I'm not sure if it'* going to be an ongoing problem. Other thing I noticed when following him during our turn tests, there is a definite discharge of bluish smoke from the tailpipe...so it'* definitely burning oil. Not sure if that means a ring problem or if it could still be the valve spring or one of the valve seals?
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Old 08-24-2010, 12:03 PM   #5
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Meant to ask too, in the event that the compression test shows a problem, is there any "simple" fix that could hold us for a month or two? Something like a higher weight oil or something like the Rislone Compression Repair oil additive? I know additives of that nature are generally not a good idea, but if I could find something that would hold until things cool off a bit (since I'd have to do any engine work in the garage and I'm not real keen on doing work in a 100 degree environment) I'd be happier.
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Old 08-24-2010, 05:59 PM   #6
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Pull the vacuum line from the fuel pressure regulator. Can you smell gas in that hose? Might all be a bad FPR
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Old 08-25-2010, 11:00 PM   #7
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Pulled the vacuum line...no fuel smell. There was however, a fairly strong fuel odor under the hood. Pulled the plugs to do the compression test, Cylinder #2 plug was wet...couldn't really tell with what but it didn't look like oil necessarily...didn't smell like fuel (or coolant) either. Wasn't able to do the compression test yet or pull the valve cover because I got rained out when my awning split. Probably have to wait for the weekend to do any more exploring.
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Old 08-25-2010, 11:03 PM   #8
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It'* likely fuel on the plug. I'm willing to bet you have no spark on that plug. Test the plug wire.
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Old 08-28-2010, 03:43 PM   #9
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Turns out the wet end of the spark plug was from coolant that was dripping down the side of the engine. The heater hose had a pinhole leak in it that was spraying a mist of coolant out whenever the engine was running and I didn't spot it immediately.

Re-tested the plug and wire, both fine. Swapped them out just to be sure and was still reading a misfire on cylinder 2. Fuel injector was swapped, still showed as a cylinder #2 problem. Did a compression test on all 6 cylinders. 1 & 3-6 were all at about 195 psi, cylinder #2 was at about 186 psi. It was the only one that was different but it'* off by only about 5%...is that a problem?

Pulled the valve/rocker arm cover, no obvious cracks in the springs or missing pieces. There was a small crack in the valve cover that was causing an oil leak past the gasket, but I can fix that.

Question though...how much oil is supposed to be on the rocker arms? When I pulled apart my old Escort engine a few years back, there was a fine sheen of oil on the rockers and valve springs. Here it is awash in oil...is that appropriate?

Any suggestions for the next step?
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Old 08-30-2010, 01:30 AM   #10
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Did you test to see if #2 injector was being fired?
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