I replaced all my plugs on my motor today and cruised a little then did one WOT pull and checked the plugs. All four plugs have a light black color on the base ring one turn around, and the ground strap is a light grey to brownish color. Those condition I believe should be fine, but then on all four plugs their are a couple black spots on the porcelein. Their is carbon build up on the pistons so could this be carbon build up, or is this knock? I Just cant believe it could be knocking in all four cylinders, is it possible its carbon build up, not knock?

 

pics?

 

I can't get any close up pics because they come out to blury. Can I just give good details and hopefully can give me an idea. The engine leak down is 2% in each cylinder btw, each plug is very identical one turn around the base ring is a light black color so im not worried about that. But on all the ground straps they have a blueish tint to them. I can see where the blue line stops about in the middle after the turn of the ground strap but before the weld right in the middle of all four. But on all four of the plugs on the porcelein there are these little blacks spots on all four. I know that detonation appears as pepper spot on the porcelein but I can't believe that it would be detonating that easily on all four, with the engine not burning oil or leaking at all. Is it possible that carbon build up will show up on the plugs, if their is excess on the pistons? The engine is also running open downpipe btw. Any advice please...