White coloring on one engine valve, what is it?

Question

I have a 88 jeep cherokee with a 2.5 liter engine. I am doing an engine head job. The number three (3) cylinder exhaust valve has white ash on it. The rest all look normal. Any ideas as to what has caused this?

Answer 1

Very lean air/fuel mixture, and got very hot because of it.
I'd hazzard to guess you had a vacuum leak near that cylinder.

Answer 2

this cylinder is burning lean. Check intake manifold for vacuum leak. Possibly a split hose somewhere else that gets it's source from the #3 intake tube.

good luck