Brand new HPFP taking a dive, while LPFP seems strong.


Mar 8, 2018
Columbia, Maryland
Car info:
2007 335i 6MT
RB next gen plus turbos
FBO- the usual
Fuel-it stage 3 LPFP
Fuel-it PI 550 injectors
FPS in-line filter/FPR with return line
LPFP sensor relocated to FPR port due to spike issues. See thread:

As described in the thread above, I replaced several fuel related parts trying to find the issue of the LPFP spikes, which I ended up relocating the sensor to smooth that signal. Never found the root cause, some say it’s the HPFP opening/closing so fast causing the issue.

Now with the spikes “resolved”, the HPFP is taking a dive ( idk if it was acting the same way with the old pump) and that is a brand new one from FCP.

To try to chase this issue, I went away from my custom tune ( since still in progress), disconnected my PI controller and uploaded an MHD OTS FF tune with e50 in the tank.

Even with only e50, targeting not even 20psi, the HPFP is diving.

Could it be anything else besides the pump causing the pressure to drop? My LPFP seems to be keeping up fine. Anyway to check the PWM signal the HPFP is receiving?

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