Boosted lsx backfiring under boost
Thread Starter
On The Tree
Joined: Jan 2016
Posts: 100
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From: Colorado
Boosted lsx backfiring under boost My engine runs great until I build 10+ psi of boost. Then it's like it's hitting a rev limiter and backfiring and stuttering. It was tuned and ran good and would do it only every now and then in 2nd gear but has gradually gotten worst and don't know what to check or fix. Anyone have any ideas?
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TECH Enthusiast
Joined: Apr 2009
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You may have a chicken/egg scenario depending on in the log if the lean reading comes before the stumble or the stumble before the lean.
A miss-fire will cause a lean O2 reading.
What heat-range are the plugs? May want to try one step warmer & see if it goes away.
What coils did you put in? Do you have an add on ignition box?
What fuel you running?
This could even be valvetrain-related.
Try & isolate if it's all the cylinders breaking up or if you have just one. Throw in fresh plugs & run it & make it miss-fire then shut it down quickly & check all 8 plugs to see how they look. If it's bad enough it will darken the isolator real quickly & at least know then if it's just one cylinder, or more than one, causing the problem.
Sounds like something wasn't right from the beginning, & now the problems getting worse.
A miss-fire will cause a lean O2 reading.
What heat-range are the plugs? May want to try one step warmer & see if it goes away.
What coils did you put in? Do you have an add on ignition box?
What fuel you running?
This could even be valvetrain-related.
Try & isolate if it's all the cylinders breaking up or if you have just one. Throw in fresh plugs & run it & make it miss-fire then shut it down quickly & check all 8 plugs to see how they look. If it's bad enough it will darken the isolator real quickly & at least know then if it's just one cylinder, or more than one, causing the problem.
Sounds like something wasn't right from the beginning, & now the problems getting worse.
Last edited by gtfoxy; Jan 7, 2016 at 08:17 AM.
^^ truth^^
Also there is a higher current demand when you go into boost. More for the coils and injectors both. Make sure the grounds for your coil packs, PCM and all other grounds aren't loose. Log your PCM voltage and look for voltage drops when it's occurring, which can indicate poor PCM grounding. GM's grounding scheme is poor from the start, so if it's compromised in the least, it can cause this. Also, check all hot-side connections as a voltage drop from either side can cause this.
Even if you believe your plug gap is appropriate, to help discover if this is ignition related, close your gaps down to .015 and see if it so much as delays your issue. If it does, it helps you know what to focus on.
Also there is a higher current demand when you go into boost. More for the coils and injectors both. Make sure the grounds for your coil packs, PCM and all other grounds aren't loose. Log your PCM voltage and look for voltage drops when it's occurring, which can indicate poor PCM grounding. GM's grounding scheme is poor from the start, so if it's compromised in the least, it can cause this. Also, check all hot-side connections as a voltage drop from either side can cause this.
Even if you believe your plug gap is appropriate, to help discover if this is ignition related, close your gaps down to .015 and see if it so much as delays your issue. If it does, it helps you know what to focus on.
Thread Starter
On The Tree
Joined: Jan 2016
Posts: 100
Likes: 0
From: Colorado
I have MSD multiple spark could with upgraded harness and I'm running 91 octane. And I've had to add grounds to the wiring harness before because I would get misfires at 4500rpm. And all the plugs don't look wet or black. The isolator and electrode look good. The ground strap has a bit of white on it though. The insulator is all white still besides one spark is tad bit darker. I'm using tr6s
Thread Starter
On The Tree
Joined: Jan 2016
Posts: 100
Likes: 0
From: Colorado
Seems better in 4th gear then 3rd and second. It doesn't backfire and all as bad but won't accelerate. And it's getting like 8 degrees KR. And we did inertia pulls and loaded pulls on a chassis dyno
Thread Starter
On The Tree
Joined: Jan 2016
Posts: 100
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From: Colorado
Well it's a brand new lsx376 B15 engine. Not saying it's not an option just cause it's new don't mean it's good but like it did this before the tune and then after the tube it went away besides every now and then at wot in 2nd gear and then I changed pcv system and it got worst and worst