popping when letting off gas

[dan2288]

I get this popping sound, like its misfiring when I get off the gas. Its usually 3k rpm and up. I have a keydiver chip set for my 880's and running br7es plugs and msd wires. What could cause it to misfire when coasting to a stop?

 

[JayRolla]

That sounds like it could be a rich condition between shifting. Are you venting your BOV to the atmosphere?

 

[dan2288]

no, its recirculated and my car is an auto if that matters

 

[92EclipseGS]

Do you have a wideband? Since you said you have your keydriver set for the 880's I'm guessing you don't know the actual A/F ratio this is giving you? (guessing its a little rich) Being on the rich side, when you let off the gas there is unburnt fuel making it into the hot exhaust at which point it "pops". It isn't much to worry about, my N/T with headers used to do this on deccel before I put a turbo/gm maf and tuned it.

If you want to fix this I suggest changing your tune to turn down the fuel slightly. A wideband is one of the few things you can use to KNOW your A/F ratio is correct. Also unless you are running a big turbo and a lot of boost, 880s are really big injectors.

 

[99gst214]

Definitely is too much fuel. I purchased my 99gst with an incorrectly installed/tuned apexi S-AFC II. The car ran very rich and under shifting conditions it made a "pop", almost like it was backfireing. This stopped after correcting the AFR. From what I could understand the sound was just un-burned fuel getting pushed through the exhaust and sometimes igniting their?!

 

[JayRolla]

Yes the fuel gets stuck in the exhaust and ignites. Causing sometimes a cool fire show out the tail pipe. Can also destroy a cat if one is installed.

This is why its always good to have an SAFC and WBO2 when using a chipped ecu. Injectors never flow exactly like they should. Every injector I have set up with the math always needs a little adjustment to get good fuel trims and AFR.

What a lot of guys do is the pull 1psi of fuel pressure out at a time and then go for a cruise and see how the trims are. Thats if you have a FPR. Its oldschool tuning. It takes fuel out across idle, mid, and WOT.

What are you fuel trims at via the logger?

 

[dan2288]

I never checked my fuel trims. But I will try adjusting the fuel pressure and see if it helps.