What would cause deceleration backfire? Like as I'm just cruising down a slight hill at normal speeds, not giving it gas, then get back on the gas it pops or backfires slightly. It doesn't do it all the time either, and seems like only in a certain rpm. My car was running like crap backfiring real bad and missing before this. At first, found a burnt #6 wire from headers, then just last week, still getting ses light, and turned out to be bad front pass o2 sensor that was solid black. Car runs a lot better now. Just a tad ruff during idle, but not real bad at all, and the backfire now and then like I said above. Mods listed in sig. Just got my tuned computer back from Ion as well.

 

1st thing, are you going from no load (0 throttle) to full load(100% throttle) at a higher rpm? you could be experiencing some leaned out knock and backfire due to how the engine control system functions....

2nd, do you still have emissions on your LT's? Any exhaust leaks? This could be causing you to run really rich, building up fuel in the exhaust, then when you nail it it lets just enough 02 in the exhaust to cause a small detonation in the exhuast...

Jonota

 

Mine does the same thing. If it's cold it is much much worse.

 

Mine too. The odd time i'll get some back fire if i let off the gas while coasting along. Very rarely, but i know that the car can run a little rich sometimes so i've learned to live with it (at least till I remove the A.I.R. system and re-program the computer next year ).
Also, it'll wanna backfire if I take it above 3grand b4 it comes up to temp, so i just take it easy on her b4 its warm.

 

My car does it as well, and I'm told that it has to do with a lack of cats. Flowmaster mufflers seem to do it too, even with a cat. My wife's car has a flowmaster and has a cat and her's does it. My car has a Magnaflow muffler and no cats and doesn't do it as bad.

I also understand that under deceleration, depening on the RPM, the PCM shuts off the fuel injectors, then when you give it some gas, it starts fueling again. when it first starts fueling, it gives too much from what I've seen in my logs and causes a little extra fuel to get into the exhaust, and it ignites there.

I've noticed on my log files that if I decel for 10 seconds, the car runs rich for 10 seconds when I get back into the gas. It's probably got to do with the car needing to go rich/lean/rich/lean to keep the cats healthy...

I might be wrong though.

 

It doesn't really "shut off" the fuel injectors, but it does go to a very small pulsewidth to try and maximize your fuel efficiency. A good test to see if it is your AIR system: look at your air intake tube on the back side near the drivers side of the radiator. There is a small tube that connects back there, this is the AIR inlet tube. Pull that tube off and plug it (plug it GOOD), and plug the hole on your air inlet. Go for a drive and see if your problem has changed....

Jonota

 

Why does an exhaust leak make the car run rich

 

It makes it run rich because outside oxygen-rich air is diluting the exhaust. The O2's see this and think the car is running lean, therefore adding more fuel.

 

That's odd, because Autotap shows a 0.00 ms pulsewidth for each bank. PLus LT1 edit has deceleration fuel cut-off settings...

 

both my freescan logs and two other peoples that i have looked at had between 1 and 3 ms pulsewidths on deceleration.... you still need to keep the engine RUNNING on deceleration, so you still need fuel

Jonota

 

If you like, I can email you an Autotap log showing 0.00 pulsewidth during deceleration.

I'm not trying to be argumentative, but trying to understand this myself, as what you say makes sense (that you need to keep the engine running).

 

mine also does this on occassion...it scares the hell out of me and anyone riding near me.

yesterday i was following a dump truck and when it backfired i saw the driver look in his mirror to see what it was! starting to get annoying though...

 

You can send if you like, but I probably won't be able to decipher why it doesn't show the pulsewidth. Look at Injuneer's PCM site, even he shows that the lowest you should expect to be around 1.4-1.6 ms. I typically see 2-3, as did GR8WHTZ in his freescan log.

Jonota