Backfire / Exhaust Popping on Decellerate - Lean?

[JNeidlinger]

So this is my first post here, as I recently bought a 1994 Mustang GT that im pretty happy with, minus some issues. The car was from an auction so Im not all that sure of its history, but its obvious it was someones project. The car had a big old monster tach sitting in the seat, with holes on the dash where it once was, and it has some shorty headers (say MAC direct replacement on them). It could possibly have some other mods, but being as I have never had one of these, no others seem apparant. It also seems to have some pretty free flowing mufflers on it, though stock cats. Other than these mods its hard to tell. The fuel pump seems to be quite loud... as its buzz is easily heard while running, so either its a stock fuel pump going bad, or someone had put in a stout pump, its hard to tell. Nevertheless, the issue is that the car likes to pop and bang on decceleration. Nothing serious at all, as a soft deceleration though the gears will prevent this or muffle it, but otherwise it does pop some. Could the car be running lean? No check engine light is ever on, and I have cleared the computer via disconnecting the battery for 10 minutes or so. Is the only other thing I could do would be to throw a fuel pressure gauge on the fuel rail and see if its correct? I've honestly never worked on these cars, nor really any cars with fuel injection and computers so I'm not really sure how to tackle it. Any pointers?

 

[JJ95GTID]

Usually the backfire/popping noise is from gas igniting from a rich condition.
When you first start the car it will run rich to help warm up the HO2 sensors and smell rich out the tailpipe.
As for the fuel pump I would bet it is an aftermarket highflow pump. The stock one is quiet and when it dies it usually does so quietly.
If the car has the stock fuel pressure regulator with a higher flowing fuel pump then that could cause a rich condition. You could solve this with an adjustable FPR.

Welcome to SN

 

[final5-0]

I agree on the excess fuel in the exhaust system causing the pops

Grady

 

[Blackened302]

i had this problem a month back. long story short:

huge exhaust leak at the collectors (X pipe wasn't tightened all the way... doh!) plus bad o2 sensors = rich condition = too much fuel in exhaust = backfire/popping/bucking

 

[Stanger007]

i had this problem a month back. long story short:

huge exhaust leak at the collectors (X pipe wasn't tightened all the way... doh!) plus bad o2 sensors = rich condition = too much fuel in exhaust = backfire/popping/bucking

I agree - check your exhaust connections before the O2 sensors.

I would think the stock fuel pressure regulator should be able to keep the pressure right where it needs to be regardless of the size fuel pump?

Wes

 

[JNeidlinger]

Wooo, alright I know I posted this awhile ago... and it has plagued me ever since. I replaced the stock FPR for a Kirban AFPR. Still no luck. Exhaust leak must be the problem, but nothing was apparent. I tightened the midpipe-header bolts up as they were lose, but they must of been tight enough because there was no change. Only other place would be at the headers, probably the header gasket? So I took off the headers and yup, the gasket at the number 8 cylinder was BURNED to a crisp all the way from the exhaust hole to the outside, all that was left was the wire mesh that holds the gasket material together. It was an improper gasket. So after blasting my headers, repainting them, new spark plugs and a fel-pro gasket, all better!

The car drives surprisingly better for a fixing a small exhaust leak. Amazing how such a small and trivial fault in the exhaust system of an engine can make it run poorly. No KOER/KOEO codes at all. In fact, I really wonder what is done to the car because it absolutely rings out, I cant even get any traction through 2nd gear. Oh, and removing and reinstalling shorty headers, not really hard, but... PITA!

 

[gcomfx.com]

Good to hear you found the problem. My car used to pop a lot. It was due to the Smog return pipe being clogged up. I had my stock cats replaced with two high flows. The shop welded the smog pipe onto the new setup and it was partially sealed. I removed the smog from the car a year later and it stopped the popping.

 

[TheDamned]

I have to find my popping problem aswell, damnit. Altough it sounds pretty badass on decel