My car has recently started to backfire horribly when I engine brake. I took out the plugs and they are white which would mean a lean condition to my understanding. Yet my muffler is black with soot which would mean a rich mixture. I know its not the ignition system cuz there is no hesitation whatsoever when I accelerate. It idles rough though. Any one have a clue?

 

Maybe your timing belt jumped a tooth. Sorry if that's not a whole lot of help.

 

I hate to tell you, but it sounds like your engine needs an overhaul. Backfiring is cause by a lack of compression and that would expain the lean condition. You're probably burning hot because you're consuming alot of oil which increases the combustion temperature by alot, which is why the plugs are white. There is black suet on the muffler because of a combination of raw fuel being burnt in the exhaust and even more so, consumption of oil.

 

I would say its your timing as well, and i would also check your fuel maps...you might be running lean most of the time and dumping a lot of fuel in some areas.

One last thing could be that your plugs are too cold or not gapped properly..

 

if you are running check valves, check em