if there was that much carbon build on the combustion chamber to cause the engine to ping, would that also show up on the plugs? There should also be alot of carbon on the plugs as well I would think. I pulled 4 of my plugs, 2 from each side, and the plugs look like brand new still. Perfect color, no deposits or funny looking stuff on them at all. Most likely they are the original motocraft plugs with approx. 48k miles on them so far