I fixed it!... but its not fixed :(

[JAM]

Car= 2000 LS 3.9 V8 auto

I recently had a check engine light that stemmed from a rough idle (low rpm mis-fire). It was an intermittent problem, sometimes it would idle fine, and then start missing, and clear up etc. It was also noticeable when it would shift into 5th gear and the rpm would drop down below about 1800 rpm. Checked the code and it said " P0305 general- misfire detected from cylinder 5", this was the only code.

Upon further investigation I learned of the valve cover seals leaking into the spark plug holes, and seems to be a pretty standard problem with these cars. I proceeded to replace the valve cover seal set with fel-pro, all new coils, all new spark plugs. Only the drivers side was leaking (of course the difficult side), but i went ahead and replaced both sides.

Upon completing the job, I find that all the seals seem to be sealing good (inside and out), however the problem is not intermittent, it has a rough idle all the time, and still has the misfire when shifting into 5th gear when the RPM drops below 1800. I know that i was not able to get all the oil out of the plug holes and some of the oil dropped into the cylinder when changing the plug. So i just went ahead and let it warm up and burn off some of the oil. I checked all the plugs and none of them were really fouled, so i just cleaned them up a bit and put them back in. Of course the problem is still there, so i reset the code and waited for another code. Sure enough, the same code popped up " P0305 general- misfire detected from cylinder 5", again, this was the only code. I did reset it several times, and this was the only code being thrown. I swapped a known good coil onto 5 and nothing changed.

I searched and read thru a few threads, one person mentioned that the misfire code may not really be representative of the cylinder it is on...??? is this correct? should I try swapping other coils on the same bank, or even on the other bank??

I guess i figure with a car with coil on plug that has a miss on a cylinder, it is either the plug, coil, signal, or the injector is not injecting the proper amount of fuel. (assuming the cylinder has compression) ???? Any suggestions would be appreciated.

 

[darkhaven]

Try swapping your number 5 and 6 coils and plug see if the code follows the coils. After that check your fuel injectors with a noid and swap your number 5 and 6 injector if still no luck check you compression

 

[pektel]

Why are there 2 threads for this?

Nice job on the diagnosis though. You are doing worlds more than most who post up with issues.

If you have a separate coil, change it one cylinder at a time, and listen for the change in idle. It is still misfiring at idle right?

 

[joegr]

If you have a consistent misfire, then the PCM probably has identified the correct cylinder. You've already changed all the coils and the plugs anyway. I also assume that you verified the gap on each plug.

I'd swap the #5 coil with #6, 7, or 8 and see if the code moves to the cylinder you swapped the coil to. If it does, then one of your new coils was defective.

If it stays with #5, then I think that your next step is to look at the #5 fuel injector. disconnect and reconnect the electrical connector to make sure that it is okay. You can use a mechanics stethoscope to verify that the injector sounds like it is opening and letting some fuel in, but you won't be able to tell if it is letting in enough or if the spray pattern is correct.

If the connection is good, then the next steps are compression and leakdown tests on #5. If they're good, then you might replace the injector as a guess at it.

 

[SlickLS]

I would check the connection on all your fuel injectors. They tend to come loose when moving the harnesses around. check them with the car running and see if it clears up.

 

[drag214]

i would check the connection on all your fuel injectors. They tend to come loose when moving the harnesses around. Check them with the car running and see if it clears up.

+1