Hey,
So I have this problem with my '95 n/a backfiring. It's nothing loud and destructive sounding. It's more of a "poom-poom". It occurs when under mechanical load and as well at a stand still when rev'd. I usally have to rev the car to around 3k before it occurs, and when I let off it backfires. It has nothing to do with the exhaust, as I have checked it myself and had a local muiffler shop look at it. So here's what is really troubling me, they said it could possibly be the emmision system.
They also said that the emission puts air into the outgoing exhaust, and that it is trapping little amounts of fuel. But how can air mixed with an exhaust stroke exiting the engine have any fuel in it? It can't... right? Unless it wasn't burning all the fuel, but I don't see any smoke coming from the exhaust. I'm pretty sure they didn't have a clue... and thought that people that are more vehicle specific would know more than couple grease *****. I couldn't find info on this subject anywhere... so far. So if guys/gals could help it would be greatly appreciated. Thanks!

 

A number of things can cause popping in the exhaust. If the car is running rich, the unburnt fuel in the exhaust tract will spontaneously ignite. The catalytic converters are also designed to cause this ignition of unburnt fuel but usually without any sounds.

The key here, with your problem, being unburnt fuel in the exhaust. There are a multitude of possible causes, anywhere from a dirty air filter to dying o2 sensors and a bunch of stuff in between. Your best bet would be to first check for any ecu codes, clean all of your electrical connections in the engine bay, and perform a basic tune-up.

 

start with checking your ECU codes like CC said, after that go do a tune up and come back tell us if it's till there or not so we can dig further into your car.

 

So I checked the ecu, and it flashed the normal condition(55).I have a brand new JWT pop-charger. so the filter isn't dirty. I also cleaned the throttle bodies.
Now I'm going to dedicate the afternoon and night to checking the sensors. I will take it to the dealer within the week.

 

You might clean the IAA unit and check closely for vacuum leaks too.

 

IAA? What is that? where is it located?

 

It's actually called the AAC valve here --->>> AAC Valve

And here it's called the IAA unit which the AAC valve is a part of. ===>>> IAA Unit.

After cleaning the IAA unit on my car, alot of my off-throttle exhaust popping went away. I now clean it every 5k miles. I have a write-up around somewhere on how I do the cleaning.

 

Ooooh, okay I know what your saying. Thanks!

I'm going to check the valve and assoc. unit . Tell you what happens when I clean it.
I'm pretty sure there aren't any vacum leaks, all the lines are tight at the moment, but i'll give it another look. thanks CC