The car is a 2002 383 LS6 block at 11:1 with H/C/I dynoed at 430RWHP and the motor has about 1200 miles since the build. The plugs that were in there were TR5GPs, and the car started developing a jerking hesitation under load. I did some research (thanks LS1TECH!) and called my engine builder to confirm, I should probably be using TR6s gapped around 0.38"-0.40" since I'm not spraying yet. So I bought some TR6s and installed them yesterday.

When I pulled the plugs, 7 of 8 were typical for the application using TR5s. However, the front plug on the DS had carbon on the OUTSIDE of the plug (not the outside of the center, the outboard portion of the plug!) The coverage was fairly thick and discreet, it abruptly cut off about 3/8 of the way up the insulator. I've attached a picture describing the situation, I'm not sure what to think. The plug wire protector that the boot fits into had a bit of the same situation going on at the plug end, but the boot inside the protector didn't seem affected.

So what do y'all think could be happening?

 

Maybe it was loose/ not sealing well.

 

Hmm, it wasn't difficult to remove, but the threads weren't similarly carbon coated. Then again, the process of removing the plug could possibly clean the threads maybe? I don't know, I was leaning more towards a header leak issue, but the plug was uniformly coated all around. It was too dark when I finished to investigate the area, but I'll do that today. Wouldn't I be able to hear a header leak?

 

Attached pictures from bank 1... WTF?

 

Looks hot

 

Ya, header leak or plug wasnt tight.

Thighten header bolts and new plugs and you should be fine.

 

Will do, I'll retorque to 18ft-lbs center out and for good measure, I'll even throw some MSD plug wires on the TR6s

 

Must have been the header bolts, the bolt closest to the plug needed plenty of turning to get back to 18ft-lbs. Thanks!

 

Closing the loop here, the header gasket was leaking top and bottom on that cylinder. Installing TSP 1 7/8" in place of the Pacesetters with new MLS gaskets