ok no matter were i go my car backfires when i turn it off. how can i stop this. all my air pump stuff is off and i have a performance exhaust so what can i do? i need to do something. i dont mind a small poof sound but a big bang i cant handle anymore. i already got warned with a disorderly conduct by the state patrol.

 

Find and fix any exhaust leaks you have.

 

if i fix all the leaks will it stop sounding like a shotgun when i turn it off?

 

It should. Fresh air sucked in thru leaks gives unburnt gas the air it needs to combust.

 

ok sounds good. thanks

 

my car has NO exhaust leaks and it still backfires every time I turn it off and high RPM decel... hehe

 

I had the same problem....
When my cats were, uh, fixed? :-) the problem went away.

Not something I'd recommend doing though, particularly if you've got to pass emissions. (though with a performance exhaust you might already be missing them?)

 

By Uh fixed, you mean taking them off? thats what i did.

 

Mine are now just pieces of pipe that resemble the once expensive catalytic converters.
(In fact, they look exactly like them, only without the crap on the inside )

 

i backfire w/ a new hi flo cat and no exhuast leaks

i just need to do my direct fire soon to solve this problem

 

my cat is hollowed out. but i do know that the cat gaskets on each end are shot.

 

Mine backfires.........since I put my RB system on and removed the smog pump.........

I can control it though.......mellow off on the down shifts......prior to shutting it off........let it idle a bit.......

If I want back fires.......get the revs up and coast.......boom.......its fun........I have all new gaskets....from header all the way back.....

 

If those gaskets are shot that could be the source of your oxygen??
They're easy 'nuff to replace....

 

When trying to troubleshoot a backfiring problem, you need to consider a couple of variables that can cause this problem, and then look at your car and see if any of these are in operation.

The guys above have done a pretty good job identifying that any exhaust leaks which allow outside air into the system will result in backfires, potentially rupturing your muffler or piping, which can result in some very serious consequences. Your muffer is a spark arrestor by design, but when you blow out your exhaust system, you're creating an open flame - open flames around your fuel tank are a bad combination. Fix any leaks by replacing the necessary piping and gaskets through a quality muffler shop. If you're using an airpump and cats, make sure that the airpump is working correctly, the cats create heat due to burning off any unburned fuel ejected by the engine. Cats concentrate this heat and with the help of the airpump, combust the fuel before it ever gets to the muffler - this results in reduced emissions. The ACV (Air Control Valve) on the side of your intake manifold controls when the airpump air is routed to the cats, so check operation of this as well.

Another cause of backfiring is commonly an overly rich mixture - not just at idle. A carb tune-up will likely help your needle valves and seats and jets work correctly after a good cleaning, and will restore fuel mileage, performance, and throttle response. This is because the air/fuel mixture needs to be almost exactly 14.7:1 ration (Air to Fuel) to burn completely. Again, any unburned gasoline is going to cause backfiring. Change your air filter, check for obstructions in the air cleaner assembly, and lube that carb up well. You may find that you need a fuel pressure regulator to help keep fuel pressure low enough that it won't overpower the needle valves that fill the bowls. If this is the case, it's a cheap fix, and may prevent backfiring and restore mileage.

The last thing to check is your timing. While most people totaly disregard timing with backfiring, if your leading timing is delayed significantly from stock settings, you're going to get poor combustion inside the engine, which will lead to poor combustion OUTSIDE the engine (i.e., exhaust system). Check and set timing according to FSM, and replace your exhaust gasket to be sure you have a good seal here. The Air Pump also directs bypass air into your exhaust ports during deceleration to help mix up the gases and burn off any unburned fuel - specifically to reduce backfiring.

Try these things out and then report back - throttle 'banging', or forcing a backfire by richening the combustion gases is dangerous, and as you've already seen, can get you ticketed. That ticket usually requires an emission test to go along with it, and they may find out that you're running an illegal exhaust system and then you're really in trouble. Those fines are nothing compared to the cost of finding and buying replacement cats that work. JMTC, HTH,

 

I had an Uncle Buck style of backfire after shutdown thanks to a 1/2" size hole between the two pipes of my long primary system's H pipe (the previous owner thought it was a good idea and forgot to weld in one small section). Stock ignition would backfire all the time, as would the MSD to a lesser extent. The backfires finally ceased with DLIDFIS.