Hi,

Just bought this 1991 Pontiac Firebird GTA and it has a the catalytic converters removed. Not sure if the exhaust is stock or not but the car is real loud! Anyways, when I am going and let off the gas the car gets some real bad backfire. Not just a little but a lot. Back fires about 8 or so times and its real loud. I believe the car runs rich but not sure, also not sure how to find out whats wrong and such. Any thoughts?

Thanks

 

any codes? timing a little off maybe?

 

It sounds like it is running rich and has an exhaust leak near the engine.

 

Thanks for the quick replys!

As for the timing and codes, I am pretty new to this kind of work so I really have no idea how to get that data?

I have an exhaust leak on my other vehicle by the motor and comparing the sound I don't believe that is the problem. Unless there is some hole or something letting in a bunch of air, but the sound comes from the rear of the car.

Thanks

 

It doesn't work like that, so you can't assume.

 

Can you please explain?

 

I think what 305sbc means is not all exhaust leaks sound the same. If you have a leak say on the drivers side the oxygen sensor will think the engine is running lean and correct for this causing the engine to be too rich.

 

Its a sonic boom from the massive power of a 305!!! J/K

If the cats are gone but the A.I.R. is still hooked up it will do that.

 

It's a HO305 sir !!!

 

Haha POWER!!!

But ok, that makes sense thanks. I suppose I will look into it. What is the A.I.R.?

 

its the stuff you breath !

 

your smog air pump...

 

So, I your going to have to explain this to me, pretty new to the whole car repair business. But are you saying that since my cats are gone, I need to disconnect my smog air pump?

 

The cats are half the A.I.R. operation so yea, i would. I got backfire VERY BAD AS WELL. Sounds like gun fire honesty. but i removed all air system, i have headers, and all new exhaust which i dont think has a leak but it could be something tiny somewhere. I have a feeling mines is running rich too. I heard that stainless steel makes the exhaust pop as well. Wish i knew what it was. HELP US!!!!

 

Ok so I was looking under my car yesterday and while looking at the exhaust I saw another metal tube that goes exactly along the exhaust. But than where it turns into connect to the exhaust it looks like the previous owner cut this connection and put a plug in the end that would go into the exhaust.... What is that tube for and could this be a problem?

 

The AIR system has a metal tube that runs back to the catalytic converter where it connects. If the CAT was removed, then the tube is either plugged or removed as well, along with the rest of the AIR system.

Backfires like you describe are usually caused by Oxygen being pulled into the exhaust pipe near the front of the system (near the engine).
It can also be caused by too little spark-advance, and/or too much fuel during decelleration. It is always made worse by exhaust leaks near the engine. The exhaust leak is where the extra Oxygen gets pulled into the exhaust pipe.

 

O, ok see that makes sense to me. Thank you! I was thinking of leaks a whole other way. I will be sure to look. Thanks!

 

i had the leak at my headers. fixed for the most part. now i have minimal backfire unless let up from under a heavy foot.