I pulled the 2nd spark plug from the drivers side bank and it was white, what does that mean, if anything? Too lean? And what would cause it?

91 4.0L v-6 163,000 miles.

Oh, and if the plugs are not gapped correctly will that cause knocking?


Thanks,

Brian

What gap are yours? Ford spec is .054".

They are gapped within specs from the sticker under the hood. I think it is .046-.054.

Brian

It is indicating an overheated plug. Possible causes are incorrect plug heat range (doubtful since it is the only one), running lean, ignition timing (unadjustble, failed test=PCM change), vacuum leaks or EGR valve (if equipped).

What harm could running lean cause? I think its been lean for a while.

Brian