Odd spark plug wear

[primered_junk]

Go to a colder plug, CR43TS ac delco is the factory plug for TBI trucks, as stated above by senator back some timing out of it. On a TBI motor you have to unplug the "timing control module" which looks like a breaker, that is what controls the advance instead of a vac advance. Dead nuts zero timing is "ideal" per GM, but any place between 0 degrees, and 6 degrees after will work. Also make sure there is no exhaust leaks, with plugs like that a burnt valve is a possibilty. The deposits are cause by the wet fuel that lingers around the exh valve in the chamber. If you can burn that fuel, your problem will burn with it.