Started getting a P0305 code misfire cylinder. The service traction control also comes on. Switched plugs, wires, cool pack around. Still same code. Did compression check all was fine. Did the seafoam cleaner and ran great for about 30 min. Then started again. This has been 2 weeks. Idles rough at times and other times real smooth.

 

A web search shows this to be a mis-fire on cylinder 5. That should narrow it down. When you say you switched wires, plugs and coil packs, did you install new ones or just switch them around ?

 

I just moved them around. It's really weird. Sometime the car run prefect and some days it throws the p0305 code.

 

If the problem stays with cylinder 5 after you switched everything out, then that most likely rules those things out. What is left ? It is possible that it is an intermittent issue with the fuel injector for cylinder 5, or a wiring issue.

 

I forgot to mention I did switch the fuel injector with another cylinder and the problem stayed with cylinder 5. I have no idea how to check/test for a wiring issue.

 

Do a compression check, probably a burnt valve

 

I did do a compression check. On cylinders 1, 3, 5, and 7 they are all at 120.

I did another can of seafoam today and the car ran prefect. That is until it was fully cooled down. I only have this problem at idle when the engine is cold.

 

I'm going to assume the engine was cold when you did the compression test.Not electrical, not a valve, is there compression loss around the spark plug threads?

 

Is this the SS V8? #5 is the first cylinder on the driver side?

 

As far as I can tell there is no compression loss around the plug threads.