Hello,

I have a Nissan S14a with SR20DET (T28 turbo, 2.5" exhaust, FMIC, horsham stage 1, walbro 255).

The problem is that the boost drops from around 5700 rpm from 1 bar to around 0.7 ar redline (the car was holding 1.1 until 7500 rpm before).
I checked until now for boost leaks, FPR, changed knock sensor, hard wired the fuel pump (this made a small difference), checked AFM, lambda, timing, still the same problem. There is no smoke on the exhaust. I am thinking of replacing the fuel pump next.
Also the problem is kind of intermitent. On rare occasions, the car is running fine.

Before hard wiring the fuel pump, I had a injector duty cycle of 107%, after that it dropped to 98% (it reaches these values for a fraction of a second just when it hits full boost, not when the boost is starting to drop).

What else could it be? Any ideas are welcomed

Thanks!

On days where it runs crappy what is it doing? or is boosting just the issue?

That's what I thought, but now, after I "played a bit" with the turbo actuator and the VVT solenoid, the car holds the boost (there didn't seem to be any issues with them, so also strange), but it feels weak on power. It feels similar to when you disable the VVT, but not all the way, or as if it would pull the timing back, but not as much as if you disconnect the knock sensor. Is it possible that the VVT is working, but not all the way? (to 21 degrees)