Backfire at WOT?

[SeX Viper]

My brother just bought a carry over 2017 LTX DX never road it and dropped it off at Hauck for a 240 tune and muffler. On our first trip to the UP it was backfiring at WOT across the lake and shooting flames out of the exhaust. It would do it every time across 4 days, we got fuel at different stations and the temps were all over the place. 2 of the lights on the dash would blink when it was happening but no code. He is getting max RPM and it is running right with our buddies sled with the same mods from Hauck, no problem running over 110 mph. It is starting and running great trail riding it only happens on long pulls. We dropped it off at Hauck on the way home and they said they have to ride it to diagnose the problem but they do not have snow so it looks like we will have to try ourselves since we are going back up there this weekend. I am skeptical that it ever got flashed or maybe a wire just didn't get hooked up? Looking for suggestions on where to start.

 

[Hammer70]

The flashing lights is your knock detection so it’s hard sounds like you have bad fuel.put octane booster and good fuel try it again.

 

[SeX Viper]

That is what we thought initially too so we put octane booster in with no results. We ran that tank really low and got gas at a different station but no luck. There was 3 sleds in our group and we all filled up at the same times all weekend so we felt we kind of ruled that out.

 

[geez150]

Does it do it while on the gas or on wide open longs pulls then chopping the throttle?

 

[SeX Viper]

Only while on the gas

 

[1nc 2000]

How much gas in the tank when doing this?
Mine did this when close to empty due to sucking air when all the gas went to the back of the tank under acceleration.