my engine began misfiring over the weekend so i took the spark plugs out and found 2 that were fouled pretty bad. they were in the #4 and #6 cylinders. #4 was misfiring, the plug was pretty much covered in thick tan/white deposits...but only on one side. the other side was covered but not quite so bad. #6 had pretty much the same thing, but not nearly as bad. The spark plugs are only 4 months old. Two questions...first, what do these types of deposits mean? i know that tan/white deposits are normal, but not this much. Secondly, how did they build up this fast...the plug went from new to fouled out in 4 months...about 8000 miles.
it is an 89 5.0 TBI...140000 miles. it pings really bad on one cylinder, i retarded the timing over the weekend but still does it even on 92 octane. it also goes through about a quart of oil in 2 weeks. (not doing too good i know)
one more thing...i failed emmissions bad...on both hydrocarbons and NOx...measured 2.96 on hydro...and the limit is .8. got 24.5 on NOx...limit is 15.0. im pretty sure the cat is shot, but could that cause it to fail that bad in both categories?

 

White deposits on the spark plugs generally indicate very high combustion temperatures. High combustion chambers will cause your car to a)ping and b)produce excessive NOx emissions. This can be caused by a failing EGR valve and/or clogged egr passages, carbon deposits on the pistons(?), and excessively lean a/f mixtures. A clogged cat can cause this as well. Just my two cents.

 

If what RedFirebird says to do doesn't fix it, try running a colder plug, first try a set that's two points colder than normal and then if it carbon fouls (black deposits) put in the set that's one point colder and see what happens.

If you're engine is unmodified then you shouldn't need to run a colder plug and the detonation you're getting is being caused by something besides a plug that's too hot for the engine, but if all else fails try a colder plug.