bonus12

Could an exhaust manifold leak cause fouling of just one spark plug while the rest show nice wear? If this is not plausible, and if the fouling does not appear to be due to oil, what else would cause only one plug to be fouled?

odonnell

Your headers link cylinders 1/4 and 2/3, in pairs.

Maybe valve guide seals? Hopefully not a ring issue.

bonus12

That's good info. Compression was great so it must be a valve seal? Not getting any smoky exhaust at all. Maybe it's just a small leak? Passed CA smog with excellent numbers.
Thanks odonnell.

thomasmryan

plug wire could be going bad..

bonus12

Thanks for that option, Could be true!