P0171; Cutting off at high RPMs

[Quad4Z26]

A little background on the car, its 3500 swapped, 5spd. Has 3.4 dohc 24# injectors, walbro 255 fuel pump, ECU is tuned for injectors and for 3500 engine. ECU was flashed by Jon (3x00-modified).

Getting DTC P0171, I delete the code and comes back up even while idling. Engine cuts off under heavy load/high rpm scenarios. Cuts off like it reaches rev limiter, after that rpms continue to climb if i stay WOT.

Doesn't happen all the time ( I'm not going WOT all the time) Under normal driving light/medium load car runs perfect.

There is times that car acts perfectly normal even at WOT. I have checked for vacuum leaks with carb cleaner, all seemed ok. Nothing seems out of place.

On cold starts engine does surge, and sounds like if it's cammed. (it is not)

I was able to get a log through my phone from a short run, car did act up, twice to be exact. I'm not sure if this would help indicate any problem.

[1988GTU]

bad injector(s), fpr clogged, maf or maf wiring, cracked uim/lim.

injectors would be where i'd start. ohm them out?

[3X00-Modified]

27% ltft and stft means its trying to add 27% x2 to the fueling and I know the tables are not that far off, you need to check what 1988GTU said, start with injectors, FPR and fuel pump... Check fuel pressure as well, it's just running extremely lean and going WOT with it like this will only hurt it.

Has it been doing this ever since you got the ECU from me?

Best things to log are,

Coolant temp
Fuel Injector Pulse width
STFT
LTFT
MAF Frequency if available, g/s is ok
Manifold Air Pressure
O2 Sensor 1
IAC
TPS
Speed
RPM
Spark
Intake Temp
Knock Retard

[Quad4Z26]

Cant really say if its been doing it that long. Car had a bad o2 sensor, had to relocate it. After it was relocated then i would go WOT, thats when i noticed this issue.

Fuel pressure at rail is 45psi IIRC, fuel pump is a new walbro unit, and new fuel filter.I guess thats leaves injectors and fpr. Will look into it in the next days. I did a maf check a few weeks ago, had to do with voltages. All checked ok.

And got it on the pids. Will remember next time i log.

Thanks to everyone.