O-Ace

Hmm, I'm guessing it would backfire if there was unburnt fuel reaching the exhaust...not enough air, but too much fuel maybe. Not sure....I'm not too technical.

Hey, that new sig pic looks nice. Reminds me of my car + euro tail lamps! :D

Ten 99

That's usually gonna be the right answer. Usually it's because you're running rich and there's unburned fuel reaching the exhaust. Have you gutted / removed your cats?

NetJunkie

Is it colder there today than it has been? Mine has been popping more now that it is colder.

Looking at your mods I'm amazed you haven't heard this before. My Z pops a lot, even with the X-pipe.


[Modified by NetJunkie, 6:22 PM 11/14/2001]

West Coast Corvette

Check for a bad knock sensor. :flag
Todd

NetJunkie

With your mods I think it is *VERY* normal. Popping with aftermarket exhaust happens a lot...headers make it even louder. If you want to soften it some try an x-pipe. That got rid of some of my popping, but then headers made some come back.

I'm not in love with it, but I'm used to it now. I've heard it on a lot of diff Vettes with aftermarket exhausts.

EHS

buckmaster:

6 posts in one hour -- sounds like you're worried and it's important.

The backfire comes from the colder weather which means richer unburnt mixture.

No worries, it's normal. Better rich than ...

:smash:


[Modified by EHS, 6:56 PM 11/14/2001]

Busted Knuckle

After this happening on the 99 the tuners all said it was puddling of fuel in the pre 2001 intake but you have a 2001 and they all have the LS6 or Z06 intake. Makes me wonder!

Busted Knuckle

Buckmaster,
It only happened on the 99 once and we had been "having some fun" on the Parkway near Eatontown NJ and we got off waiting on a friend and when I restarted the car "Pow" and that got me to talking to a lot of guys who do the Vette Dr's and CARTEK and the word puddling came up. It scared the Crap out of me but when I cranked the motor again all was fine. I have an butt load of mods on the motor so maybe your AIR/Fuel needs looking @! Mine has never done it since! :cheers: :flag

clem zahrobsky

check your exhaust for leaks as this will let air into the exhaust and cause the backfire.


[Modified by clem zahrobsky, 9:00 PM 11/14/2001]

C5Noir

Buckmaster, here's "backfire" from my ASE Certification manual:
Backfire - is caused by the air-fuel mixture igniting in the intake manifold or exhaust system. A loud BAND or POP sound can be heard when the mixture ignites.
Backfiring can be caused by incorrect ignition timing, crossed spark plug wires, cracked distributor cap, bad carburetor accelerator pump, exhaust system leakage, faulty air injection system or other system fault.

Maybe that can steer you toward a solution :)

C5Noir

Buckmaster, it could be your TTS program. The A/F and timing could be outta wack with the decrease in ambient temps. I would check the exhaust first. Do you have autotap? You could get some runs with it and see where you LTFT and Timing is. :seeya

CarolinaC5

Does the engine feel a little rougher? Mine was backfiring every once and awhile and running rough. I took it to the dealership, turns out it was a bad spark plug causing misfirings.

Tom

PS. This started at about 13000 miles.

C5Noir

That is very possible. I would check all of your exhaust for leaks.

team-zr1

Bingo ... and the cat protection of EPA functions in PCM is not going to like it, rich is a no no to cats.

OPEN PLZ

I have had plug wire burns an number of times, after 20K miles I have remedied the situation. Sometimes the first indicator of an early burn is backfiring, the next thing I ussually notice is poor performance from 1500- 1700 RPMs

Good luck
Greg

Speed-Racer

I wonder how "loud" this backfire is. I have heard some that sound like gunshots. Mine always gurgles but not pops unless I slow down by being in a low gear on the auto. You mean that sort of sound?

My guess I would buy the autotap (or whatever utility) and get some recordings.

Speed-Racer

team-zr1

Being that changing the PCM code was the last changes you did, dumped PCM NVram and RAM, causing the engine management to go through a relearn process, it now might show the AFR is not what you want.

We can guess but the best path is to hook up a PCM scanner and see exactly how the fuel trims, timing, knock etc look like and if there is any pending DTCs hiding out.
Also via scanner, run the I/M tests results function and see if emissions are in a passed completed state.
EPA wants to protect the cats, thus backfires are not wanted and thus that condition will cause PCM to protect cats by detuning to prevent more backfiring from doing damage to cats.

The scanner would allow you to have hard facts as what all 4 O2s are reporting and downstream ( after cats) 02s should on cold start clearly show lower mVolts then their upstream partner since Cats output O2.


[Modified by team-zr1, 2:46 PM 11/16/2001]