Tuning issue or vacuum/boost related?

[jey_253]

I have a ca18det with a fmic, sr t25, and z32 fuel pump/filter. Car pulls a lot stronger and smoother but with stock ecu im gettin weird power loss from about 2.5-3.0k up till i hit boost or 4k. Feels like either lean spot or timing being retarded. only does it with low throttle imputs. what could be the problem here.