Breaking up at 4k rpm turbo Brz.
 

Car developed a problem with breaking up and backfiring at 4k under boost. Ideas? 9psi, 550cc injectors, in tank 255, logs show the afr unstable and towards the lean end at about 15.1. Not going into boost until resolved. Issue started with occasional pop, now will not rev past 4k under boost. Threw a multiple cylinder random misfire code.

What are the MAF voltages doing?

e85?

DI seals?

The Frozen North

I would start with verifying in tank pump install/ pump taking a shit. Second thought is destroyed DI seals.

Quick test. With car idle, if you blip the throttle, do you get firecracking pops?

If yes, hints at DI seals, if not, hints at you are going really lean because of improper pump install. I'm inclined to bad pump or wrong install letting fuel pressure leak out of O rings.

Nice second post. Can you post up said logs? Who is your tuner?

Is the car only leaning out and misfire as you come into boost? Can you lightly drive up to the 4k+ rpm range without issue?

Reason I ask is because my car has similar issue when it's colder outside at around the same rpm, no matter the engine load or boost. Been chasing the issue for a while now and it's looking more and more like the MAP sensor. Changing nothing except the MAP scaling and switching back to stock MAP sensor fixed it for me but I can't actually run the stock one due to it only reading like 5psi. I know some of the innovate guys are/were also having similar issues.

Check your spark plugs, and also for vacuum/boost leak.

Didn't somebody have an issue with the coil packs failing and causing these types of issues?

I think that was csg? I dont remember his full name

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@CSG Mike?

Log with equivilance ratio requested afr. And fuel system status. Sounds like you are running in closed loop with bad injector scaling and maxing out fuel trims.

Post any logs you have for is to review and I sure we can figure it out.

If the car ran good for a while, than started having issues out of nowhere it probably isn't (directly) the tune.

Misfire code is telling me check the plugs/coilpack and you will probably find your issue. If that doesn't turn up anything check to make sure your wiring didn't get burned resting on something hot maybe? Or the wires accidentally ripped out of a connecter.

I actually completely misread the OP earlier. I thought he said he was getting sputter past 4k when hitting boost. I didn't realize he meant it will no longer rev past 4k.