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GMC Envoy Cylinder Misfire

3 messages,  Last post on Dec 03, 2009 at 10:15 AM

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#1 of 3 Cylinder Misfire by fire93 Apr 23, 2009 (12:22 am)
I have a 2005 Envoy 4.2 I6. About 2 years ago we had the ECM replaced with our extended warranty because it was throwing codes. Just recently it started to throw codes. I hooked the computer up to it, and it is reading P0305-cylinder 5 misfire. I replaced all the spark plugs with Bosch Platinum 4's and cleared the codes. The same day, it threw the same code. So I got a new coil and replaced the one in cylinder 5. Again, cleared the code and came back. Took the new coil and moved it to a different cylinder to see if it was the coil and still getting the same code. I have tested the battery, which is sitting within normal range. Hooked a ground wire from the ECU to a different ground to make sure that there was an adequate ground and got nothing. I have looked at the graph on the computer while the car is running and all injectors are pushing the same amount of fuel through them. I am at a loss of what to do. Can anyone help steer me in the right direction? Replies to this message: mhage (May 09, 2009 8:17 pm) tmrut0211 (Dec 03, 2009 10:15 am)
#2 of 3 Re: Cylinder Misfire [fire93] by mhage May 09, 2009 (8:17 pm)
Replying to: fire93 (Apr 23, 2009 12:22 am) I brought my Envoy in and they came back later and said that I had the same problem. Without my permission, they also ran a leakdown test and claim that I have something going on with that same cylinder (stuck valve, broken valve spring, scored cylinder).
#3 of 3 Re: Cylinder Misfire [fire93] by tmrut0211 Dec 03, 2009 (10:15 am)
Replying to: fire93 (Apr 23, 2009 12:22 am) Had a similar problem on an '02 Envoy. I racked my brain trying to figure out why I had a misfire on cylinder 4. Nothing would make it go away for long. One day, I had the intake plenum off and had the car running. I wiggled the wire at the connector to the coil. It would make it fire or misfire. As it turned out, it was a broken wire going into the connector. Bought a connector with 6" pigtails at the wrecking yard, replaced it and the problem went away.

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