I drive an 84 camaro z28 with a 305 engine (automatic tranny) with dual exhaust flowmasters with echo chambers. Thats all I know about the exhaust because it was already on the car when I bought it. When I am slowing down the car always makes a popping noise out of the exhaust pipe when it shifts down into first. It dose not do that in any of the other gears just first and it makes the popping noise only when I am braking into first it dosenot occur when I am upshiffting. I am going to say its the muffler that I have that is making the popping noise because a couple of other cars do the same thing down my street. But I dont know...

 

A friend of mine said the air pump (smog pump) could cause the backfiring in the exhaust system.

 

The A.I.R. pump isn't doing anything to cause this.

It's typical of a slightly rich mixture, and having a loud muffler will let more of the noise out. It's happening in first only because the car is dragging the engine along more in the low gear than it does in the higher gears.

 

Yup, the A.I.R. pump is only in play at cold start up. But if something is melfunctioning in the A.I.R. system wellllllll.

Auggie

 

Like 57 said, what your describing is typical of an engine that is running a tad rich and has a fairly open exhaust.

Nothing to be worried about, but if you really dont like it i would start looking on the carb board for tips on tuning the q-jet, granted thats still whats on there

 

I took the belt off the smog pump and I drove it and the popping decreased considerably so thats what the problem was.

 

You never said if you still have an O2 sensor but if you do and the EDES air control valve in the A.I.R system is melfunctioning you may be pumping air from the air pump into the exhaust manifolds at all times. The O2 sensor would see a lean mixture and call for more fuel. If you still have cats this would overheat them and cause after burning or poping noises. Were any codes set??

Auggie