Okay this is my first time posting! I have searched everywhere for this problem and nothing seems to help. I have a 2007.5 Sierra 1500 4x4 5.3 with a 76mm trick turbo kit. 4l80e swap. Texas speed cam, ls9 headgaskets, arp head bolts, alky meth kit, 60lb injectors, valve springs.When I get into boost it backfires and falls on its face! The truck was tuned last year with stock motor and stock transmission and turbo kit running 8psi and it ran mint! Over the winter I rebuilt a 4l80e and swapped it in the truck and cranked the boost up to 11psi and added the meth kit. Brought it to my tuner and and he said the valves were floating and it had a slight pop/backfire into boost. So I had him put in valve spring (I believe they were pac 1218). Then went to tune it again and a valve dropped on cylinder 7. It didn't damage the cylinder wall so I put in a new piston and two new valves along with a cam and new timing chain. It idles and drives fine out of boost. But backfires when I get into it. The tuner said the backfire appears to be getting worse.

The things I have tried.
• new ngk tr6 plugs
• swapped coil packs with another truck
• checked my fuel pressure (doesn't drop when backfires)
• did a leak down test all cylinders were good
• sent the injectors out to get flow tested ( some were sludged but backfire is still there) all injectors were rebuilt
• changed cam and crank sensors
• unplugged meth kit.....issue still there!

Any help would be appreciated! Could it be something with my transmission or something with the swap? Thanks in advance!

 

What is the AFR when it happens? What gap are you running? Could be blowing out your spark.

 

I'm not sure on the Afr it's still at the tuners shop. I'm running .028 gap

 

Would have to see the tune file to say if that is the issue or not.

Otherwise I'm not sure.