Im posting on behalf of a friend. I thought i was skilled enough to figure out his problem but i cant for the life of me.
So the engine sputters, pops from the exhaust and cuts out when boost goes above 8-10psi (sometimes it does it up at 18psi). It happens at about 4000rpm+. The car drives and idles fine apart from when boosting. Before all of this suddenly happened he was getting 550-600ks to a tanks. Now he struggles to get 400.
Forged bottom end (20000ks since build)
Some precision turbo (equivalent of gt30)
Haltech ecu (built-in MAP sensor)
Walbro 255 (brand new)
Full 3inch straight through exhaust
The problem comes and goes.
Something to note is that the car was tuned with a kakimoto muffler in place and have since deleted it making the system straight through.
We did a boost leak test and a smoke test. Both showed no leaks.
We have checked the TPS and had it calibrated by the ecu.
We replaced the spark plugs 3 times from bkr7e to bcpr7es both gapped at 0.75 then down to 0.6 with no luck. The bcpr's made the problem occur more often. Something to note is that the spark plugs came out white all 3 times. We also tried other coilpacks with no luck. We also checked the ground on the coilpack harnesses and it was like new.
We replaced the fuel filter and fuel pump with no luck. We also checked the FPR and it seems to be working fine. We replaced the oxygen sensor even though it doesnt function above a certain rev. The old one came out really white as well. We even tried unplugging it with no luck.
We have exhausted our options. He has come to a point where he will just give it to his tuner (unigroup) to deal with it and hope for the best (price wise)
My mechanic (not his) reckons its tune related, ignition timing related or the injectors are shitting themselves (i thought bad injector symptoms were different)
Does anyone have any suggestions?