Are you running a fuel pressure sensor? I have the AEM FPR and a SOS fuel pressure sensor kit with AEM Fuel pressure sensor and i am having semi erratic readings as well. Not sure if its the FPR or the fact that I didnt receive the buffer that goes in between the stainless line and the pressure sensor.

 

I have all that. Did not install the "buffer" either. Can u goninto some detail of the behavior so i can compare. Btw the buffer wouldnt allow me to tighten the fitting enough to NOT leak so i applied more pressure to tighten and it about stripped the npt fitting. Probably some frustration relieved by not receiving it lol.

 

The readings were never a nice steady rate, even at idle. they would bounce around from 34-38psi and we could never truly "set" base pressure. Also during a WOT pull it would fluctuate +/- 10psi. I have a feeling it is the lack of buffer because that npt fitting is cupped to seat nicely with that piece. Glad I'm not the only one in this boat lol. I need to increase fuel pressure as i hit 100% inj duty cycle at 8200+ rpm.