Downhill Coast Down Backfire

[DougD]

I've got a truck with the GMPP 430hp LS3 crate engine which has a rare but very persistent backfire problem when we take it to the top of a mountain pass (approx 12000', we are in Colordao) and coast downhill. After you crest the pass and start down the other side the truck will occasionally have a significant exhaust backfire out the tailpipe. I can watch the O2 sensors, open/closed loop and decel fuel cutoff on my scanner and during coasting if the truck is in closed loop the backfire won't happen. When it goes to decel fuel cut and is in open loop the O2 sensors go dead since everything is in cutoff mode and I'll be coasting along and all of a sudden I'll see an O2 spike up to around .8V and the truck will backfire (all while still in open loop decel fuel cut mode). Often the spike has been only on bank 2 but today I did once see a spike simultaneously on both banks.

I'm not sure what determines when it goes in and out of decel fuel cut but it seems to only happen in that mode when it's open loop. When it's closed loop I'll hear typical exhaust burbles and crackles but no significant backfire. Two questions...

Does anyone have any suggestions what could be causing this?
Is there any problem with turning off decel fuel cut so we don't have the backfire as a work-around?

[Cringer]

I've got a truck with the GMPP 430hp LS3 crate engine which has a rare but very persistent backfire problem when we take it to the top of a mountain pass (approx 12000', we are in Colordao) and coast downhill. After you crest the pass and start down the other side the truck will occasionally have a significant exhaust backfire out the tailpipe. I can watch the O2 sensors, open/closed loop and decel fuel cutoff on my scanner and during coasting if the truck is in closed loop the backfire won't happen. When it goes to decel fuel cut and is in open loop the O2 sensors go dead since everything is in cutoff mode and I'll be coasting along and all of a sudden I'll see an O2 spike up to around .8V and the truck will backfire (all while still in open loop decel fuel cut mode). Often the spike has been only on bank 2 but today I did once see a spike simultaneously on both banks.

I'm not sure what determines when it goes in and out of decel fuel cut but it seems to only happen in that mode when it's open loop. When it's closed loop I'll hear typical exhaust burbles and crackles but no significant backfire. Two questions...

Does anyone have any suggestions what could be causing this?
Is there any problem with turning off decel fuel cut so we don't have the backfire as a work-around?

There are no issues or problems disabling DCFO. Disabling it may help in the meantime, but this is really just covering up a symptom of a different problem that should be addressed. Are you using the stock LS3 cam? Who did the tune?

[DougD]

There are no issues or problems disabling DCFO. Disabling it may help in the meantime, but this is really just covering up a symptom of a different problem that should be addressed. Are you using the stock LS3 cam? Who did the tune?

Thanks for the input, the engine is a completely stock out of the crate LS3. A small tuner in Denver did the tune on it, he's on vacation at the moment and should be available to assist when he gets back.

[pannetron]

Also check for any exhaust leaks, even a tiny one.

[DougD]

Well here's a new one on me... seems to be resolved and it was caused by a loose ground. I saw some erratic readings on the oil pressure sensor channel. Checked all my grounds and found the battery terminal a little loose. Since then, no backfire.