GlennSullivan

Stock C6-Z06, Owned Since New, 13,000 miles. Heads Not Reworked.

CEL and engine misfire started during a hard 3rd and 4th gear run.
No unusual mechanical noises.

Pulled Codes
P0301 Cylinder 1 Misfire Detected.
Pulled all the plugs on drivers side 1,3,5,7 all super clean and dry of fuel and oil.
Checked plug gaps all at a tight .040.
Put borescope into each of the drivers side cylinders, did not see anything unusual except for carbon buildup on piston tops on all 4 (see pics)
Ran compression test on all 4 drivers side cylinders 1=215, 3=206, 5=206, 7=206.
Have not pulled the valve cover, was thinking that if there were valve issues causing misfire, I'd be getting low compression.
I think the next thing I'm going to do is swap out the coil on the #1 cylinder.

Your thoughts: Thanks for any insight you can provide.

ClothSeats

Sounds like the mechanical parts are OK, so I would suspect either ignition or fuel. Is the misfiring bad enough to cause rough idle? If so, you could back probe the #1 ignition coil primary with an LED test light to see if ignition signal is consistent or not. Then do the same with the fuel injector.

GlennSullivan

I've never done that before, I have a spare new coil and an inline spark tester. Can I accomplish the same thing by installing the spare coil and spark tester and confirm spark? If not, can you point me to an article or post on how to do the back probe?

ClothSeats

You could use your spark tester on #1 cylinder now before swapping in your spare coil. If you get a spark, and it is consistent at idle, then that would indicate the #1 coil is good and the signal coming into the coil is also good, so there would be no need to swap in your spare coil. Only swap the spare coil if the spark tester shows that the current coil doesn't produce a good, consistent spark.

GlennSullivan

Makes Sense. If there is weak or no spark on #1 coil / plug, then I'm swapping the coil and possibly plug wire if needed. If spark is good on #1 with the original coil/ wire/ plug, then that would point me to the injector or injector firing.

When looking at the plugs, they are super clean and identical on 1,3,5,7, which would kind of point me toward the injector, if it was ignition, then the #1 plug would be wet or dirty getting fuel and not firing.

Going to follow the ignition first test tomorrow and update.

0Tampa Tuning

Rarely is it the coil pack. Most of the time its the spark plug wire, then the spark plug.
The weather up north have been pretty cold, so hopefully it didnt cause an issue with the valve spring.

Bob570

Spark plug wires.

Same thing happened to me 2 months ago after a pull 1st-4th gears. I replaced the spark plug wires and cleared the code, problem solved.

C5 Diag

I’ve done a video on a coil pack functional check concentrating on the signal wire which I linked below…all these 4 wire coil packs operate the same way…I misspoke in the video saying you’ll see a 0-5 volt square wave with a scope…it is a 0-4 volt square wave…you may have a good spark at idle but under load when the cylinder pressures are higher the spark may break down..coil packs on these LS platforms are pretty robust but changing it is your choice…you can pull off a valve cover and check the #1 cylinder valve springs…you can also look at your long term fuel trims…an injector misfire will have elevated long terms around 15% or so…if you have a fuel pressure gauge and an injector tester you can do an injector balance test or just swap the injector with a known good…without some specialized diagnostic equipment the best you can do is “swaptronics” !!