For some reson my car will backfire ALOT if I rev it up and let of the gas. Or if I am say holding it in gear and let the engine slow the car down from 3000+ rpms. I know some backfiring is probly normal. But it is rediculess at how much it backfires. I can see flames come out the exhaust!
The car doesnt seem to be running rich i dont think. But the previous ownder did say there was LT1 injectors in it. I am not sure what size differance they are or if it maters.
Mabe timing??
any help would be good people ask me to rev it up all the time (sounds good) but it is imbarssing when i let off the gas and it sounds like a 50 caliber rifle going off!

 

my 91 LB9 did the same as well. i later figured out 3 injectors were stuck open dumping raw fuel in (runnin ***-rich), and my cat was non-existent. the cat should burn off a lot of that unburnt crap, reducing backfire.. start with the injectors, if you have a 305 you should have 19LB injectors and nothing more or less, unless you want to mess with the engine computer. if it's a 350, i think its 21LB injectors stock? i dont know

definitely check into the injectors- get those done first BEFORE the cat, over time the unburnt fuel will plug the cat and render it ****ed

 

stock 305 is 19lb injectors, stock 350 is 22 lbs... anything different from that you NEED to have your prom reprogrammed

 

If your AIR system is still attached, make sure your diverter valve is working. It should divert (vent) air under the hood rather than pump it into the exhaust on deceleration.

An exhaust leak near the front can do it too as it will draw in air on decel and ignite unburnt fuel in the exhaust stream.

 

so the exhaust popping suggest a rich condition or a lean one?