Mastif

Guys,
I am stumped, and need opinions. New Supercharged, forged LS engine with 5-6K miles on it. Runs great, with no issues. I just removed the plugs while doing some maintenance, and found all plugs to look new, except for #4, and it is Dry, Black Sooty. Here is everything I have done so far.

Installed 8 new plugs
Installed new wires
swapped the coil to other bank
swapped the injector to other bank
compression #4 test show same as other cylinders
Sprayed starter fluid for air leaks.

After all these changes and test, the plug #4 repeated.

Not sure where to look now other than pull intake to inspect, then head, then piston????? ANY SUGGESTIONS is appreciated.

Ryans99ls1

iTrader: (16)

If you swapped all of those and the symptom stayed on #4, start checking your wiring on that cylinder. coil and injector. trace it all the way back to the PCM

Monte4ever

iTrader: (2)

Place one probe of an ohm meter on the hot side of the #4 injector wiring harness and the other probe on the injector fuse teminal at the fuse box. At least you will know if it's good up to that point.

Mastif

Thanks for the suggestions guys, I will get back on it in the morning and see what I can find.
I am posting a pic to give you a better idea of what the plug looks like, and like I said, 7 look great, and only the #4 pictured on the right is a issue.
This is dry sooty, not oil.

Blown06

iTrader: (32)

Motor might be hurt. First thing I would do is a leak down before you hurt it any further. If the leak down checks out okay, then you can start troubleshooting with it running.

Bad Apache

Wow no drivability problems with a plug like that. I agree with a leak down test first. Testers are cheap if you don't have one. Compare #4 with some others as a basis. Have you had any oil consumption? The plug sure looks like fuel fouling though. You can check dwell with a multi-meter on the injector and compare with others as well. A quality spark tester would let you know if the ignition system is up to snuff. Every cause I can think of would cause a drivability concern, lol. Good luck!

Mastif

Thanks for all the input guys, I am now in the process of doing a leak down.
Question, If the rockers are off of the the engine, can the leak down test be done with the piston in any position, or does it still have to be TDC?

Bad Apache

TDC should not matter with the rockers off. Leak down is done with minimal pressure, but it still may push the piston down. The results would be credible either way, barring a cylinder wall flaw low in the cylinder (very doubtful).