So I was decelerating towards a stop light (engine braking), when my car backfired extremely loudly. It backfires alot, but not usually anywhere near this loud. After it backfired a huge puff of oil smoke came out of the exhaust until I started moving again. There really isn't a power difference, however there is a slight hesitation when going from light throttle to WOT, but I think that was happening before this, I can't remember. I'm going to do a compression check tomorrow hopefully. It's an 86 GXL with full exhaust.

 

When I had this problem, the culprit was a sock in my gas tank...

Sock as in 'Reebok' not as in 'sieve.'

 

Pull codes...
Check operation of the AAV (anti-afterburn valve) and air pump per the FSM procedure.
Check O2 voltage during decelleration; should be less than 0.45 v (lean).
Check/set idle mixture per FSM
Check/test/set TPS, AFM, intake air temp sensor, water thermo sensor