At 60,000 miles the check engine light came on. It sometimes flashes, sometimes is solid, sometimes does not effect performance other times shuts down fuel to the cylinder and runs very bad. Can correct itself and then run good. Cleared codes and might be good for 15 minutes or 15 days but always returns. I run a very large Mercedes-Benz dealer service department and have for over 30 years so have quite a bit of tehcnical background. When we check the codes it is always showing a code for misfiring on #2 cylinder and further shows many misfires occuring most of which you never feel but at times will be severe. I have replaced the coil on the #2 cylinder, the wire from the coil to the spark plug, all spark plugs, the fuel injector on the # 2 cylinder, the small wiring harness for the coils. I have ran compression check an all cylinders and it is good with all cylinders exremely close. Ran cylinder leakage test on # 2 cylinder and it is also good. Took it to local Chevrolet dealer and they replace the ECM under the emissions warranty and the checke engine light was on again 2 days later with same misfire code. Have checked all the wiring for any chaffed areas and find none, have tried moving wiring harness around to see if problem can be duplicated without success. Used a boroscope to look inside the # 2 cylinder and the everything looks good. Ran some decarb through just in case there was any carbon build up that I could not see with boroscope and light came on again a day after clearing the codes.
I need some ideas as I have finally given up and just parked it in my garage and not driving.

Wow, you sure have done alot of diagnostic work on it! I know this may be a longshot but have you checked your crank sensor? Other than that I would guess that there might be a bad ground somewhere. Keep us posted and good luck, I know it can be frustrating when you can't find what's the problem.

Greg.

Check the grounds both sides of the block, and the back of the drivers side head. When you pulled #2 plug how did it look?? Did it have any oil on it?? If so you may have a bad valve guide or valve stem seal. Then you would have to pull the intake and look down the intake runner to see if there is oil on the back of the valve. Then when the valve opens the oil goes in the cylinder and fouls the plug causing a miss. I have see this but mostly on ported heads that were not done right. Good luck.

The spark plugs (and #2 cylinder all looked good) no oil deposits. I also pulled the valve cover just to make sure that no valve spring was broken. With the boroscope i was able to see the backside of the valve and no oil or havey carbon deposits. The nature of this problem and the way it occurs sure points to electrical but just cannot seem to locate.

Any particular RPM this happens or begins to happen, I'm thinking something odd like a weak valve spring.

I'm sending you a PM...

Does not really seem to be RPM related. I have had the check engine light come on at very low RPM's (under or around 1800 to 2100, with either feeling a misfire occur or when I did not feel a misfire occur. At other times I have felt the misfire occur and then the check engine light will come one while driving at freeway speeds.

Thanks for the reply though and I look forward to any suggestions or help.

Did you check your Mass Air Flow Sensor?? Sometimes if you run an oiled air filter and it is over oiled the oil gets on the thin wires that read the air flow and throw it off. Spray it with a contact cleaner, do not touch the wires or wipe them just spray them. You can get the contact cleaner at Radio Shack or Home Depot. Also what plug wires are you using?? I have had problems with MSD.

Something I'm not too familiar with but may cause a problem is the Optispark.... Have you checked it?

1996 was the last year for Optispark, thank god. That was replaced by coilpacks.

I have not run an oiled air filter however I had thought about the air mass sensor as we have had issues from time to time on some Mercedes with them. Sprayed it with the same contact cleaner we use in our shop on our Mercedes. When I replaced the coild pack and fuel injectory on the #2 cylinder I also replaced the plug wire with an original factory wire (bought the coil pack, injector and plug wire from one of the local Chevy dealers.

The part that makes me think it is electrical, is that it does not do it all the time. If it ran bad all the time and showed a misfire on a certain cylinder I would tend to think possible bent pushrod, if you shifted 3rd to 2nd or 4th to 1st with a manual transmission which I have seen happen especially with the factory shifter. I have also seen this on automatic transmission when people manually shift. I have seen pushrods bent badly or even broke and the car still runs, just not real well. Maybe you want to look at that. Try to find someone who can check your fuel trims using EFI Live. Maybe something will turn up there. Good Luck and don't give up. Keep us posted.

:lol: Showed my age on that brain fart! Anyway I think Blu is heading where I meant to go, electrical, as a meachanical failure SHOULD be consistantly bad.

This is where I'm in a grey area on these cars. HOW does the car know when to fire a cylinder's spark plug?? Is there a cam sensor ect...

Can you get access to a Tech 2 and have the engine monitored while it's running? What codes are you throwing anyway?

You have a crank position sensor and a cam position sensor.

Yeah that's what I kinda knew actually. Sooooo any way those sensors could be faulting on only one cylinder? Sounds unlikely but I'm running out of options for the poor guy.

Dale, did you get my PM about contacting Paul?

Yeah that's what I kinda knew actually. Sooooo any way those sensors could be faulting on only one cylinder? Sounds unlikely but I'm running out of options for the poor guy.

Dale, did you get my PM about contacting Paul?

No, if the crank position sensor goes the car will not start. If the cam position goes the car will also not start. If the cam moves due to the retaining plate coming loose, GM did not use locktite on the early models, it will throw a code and the car will go into limp mode or shut down. But it will not affect only one cylinder.