LS7 backfires at idle?

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Jan 22, 2017 | 10:38 AM

Bowtiejoni

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LS7 backfires at idle?

Hi guys,
I have stock crate LS7 with gmpp pcm. Headers and 3" pipes with short borlas.

After cold start, it bangs/backfires 5-10 times. Could it be too lean due high flow exhaust?

Any ideas?

Jan 22, 2017 | 10:59 AM

brandon6.0

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From: Glennville, GA.

any codes? Could be a number of things. Does it actually crank up fine? changed plugs?

Jan 22, 2017 | 12:44 PM

Bowtiejoni

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Quote:

Originally Posted by brandon6.0

any codes? Could be a number of things. Does it actually crank up fine? changed plugs?

I have not had change see any codes yet. Zero miles so far on the car. Brand new engine. It cranks up really fine but dont start immediately at cold.

Jan 22, 2017 | 02:55 PM

Darth_V8r

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Exhaust backfire or intake backfire? If exhaust, check for leaks

Jan 22, 2017 | 03:34 PM

Compsystems

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Quote:

Originally Posted by Darth_V8r

Exhaust backfire or intake backfire? If exhaust, check for leaks

If it does this during cold start then its in open loop, and not reading the 02's yet. So exhaust leak wouldnt matter at this point.

Does it have the same backfire after it warms up or after a hot start?

Its most likely a fuel supply issue causing it to run lean. Check your fuel pressure at the rail and see if its within spec.

Also make sure all sensors are plugged in including the MAF.

Last edited by Compsystems; Jan 22, 2017 at 03:42 PM.

Jan 22, 2017 | 03:57 PM

Darth_V8r

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It would if its dumping fuel, sucking in fresh air, and then igniting the in burnt fuel.

Jan 22, 2017 | 05:42 PM

brandon6.0

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From: Glennville, GA.

^^ yes that is possible. Your best bet at this point is to get u a wideband on that thing and see whats going on. It should be in the low 13s on a fresh cold start and work its way up to 14.7 when it goes into closed loop around 150*.