# 2006 LS2 decelleration backfire



## epoxy1 (Sep 1, 2010)

I have a 2006 stock LS2 out of GTO in my Chevelle, I'm experiencing a severe backfire on hard decelleration. The car has been on a dyno three times and they can't seem to find the problem. I have had the injectors cleaned and leak tested and still have the same problem. 
Has anyone had a similar issue that could provide some input?


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## Poncho Dan (Jun 30, 2009)

Sounds like DFCO (Deceleration Fuel Cutoff) is still disabled from tuning. If DFCO is set to stock, it should engage all the way down to 1200RPM, which is when you'd normally hear it backfire.


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## epoxy1 (Sep 1, 2010)

I,m not sure how the DFCO is set up but the car will backfire around 3000 rpm's if it is run up to 5000 or more. 

Is there any possibilty it could be mechanical failure or a crank sensor acting up?


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## Poncho Dan (Jun 30, 2009)

No way to tell without a data log or at least a scanner that could read live data.

Is it 100% stock, cammed, just bolt-ons..?


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## epoxy1 (Sep 1, 2010)

Yes, it just has long tube headrers and an air intake.

There is one other thing, the engine is running at 180 degrees abd I think in the GTO it runs about 210 degrees. Should I be running a hotter spark plug.


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## jpalamar (Jul 22, 2008)

You have a modded exhaust. Some backfire will happen with longtubes especially if your catless.

Also an exjaust leak somewhere could cause this.

Mine does it when I go hard on the throttle and let off abruptly and then anytime the RPMs go arround 1200ish. DFCO is enabled on mine.


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## svede1212 (Nov 1, 2005)

Backfire with deceleration fuel cut off enabled is cause by the the leaning of fuel when under low throttle position (low manifold pressure). Oddly enough you can minimize it by aggressively cutting off fuel under those conditions with the tune. I have my VE table set so that MAPs under cruising conditions rapidly go to extremely lean and that almost completely eliminates back firing as there isn't any fuel left to do that. The other way is to totally disable DFCO (not recommended) and the richness of the tune will eliminate it also. As to your engine temps the thermostat determines coolant temps and the stock temp is in the low 190s normally. It sounds like someone replace your stat with a lower temp one. That isn't the problem for backfiring tho


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## epoxy1 (Sep 1, 2010)

Thanks for the input.


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## epoxy1 (Sep 1, 2010)

If I put high flow cats on the car will that eliminate the backfire?


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## jpalamar (Jul 22, 2008)

epoxy1 said:


> If I put high flow cats on the car will that eliminate the backfire?


It will help. I doubt completely eliminate though. Having the tune corrected will do alot more


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## GM4life (Mar 18, 2007)

epoxy1 said:


> If I put high flow cats on the car will that eliminate the backfire?


Modded exhaust will increase the sound of the backfire, quieter exhaust will mufflle it some. Adding cats won't do much, I have stock cats and still have backfire. If I put my LMI's it is much louder, go back to my Magnaflows its still there but muffled greatly. You just have to understand the backfire is caused by unburnt fuel being dumped and ignited in the exhaust during decel.


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