I just discovered today that my fuel pressure falls with moderate throttle. It seems to do it mostly in the lower-middle rpm. Its falling from 39 psi to about 32 psi. The pressure is set to 43.5 with the vac line off. Is this the pump or regulator going out? Fuel filter maybe? Its a Walbro 255 intank and a Holly FPR. I have had the pump for about 5 years. It has always had the infamous problem of not holding pressure with just the key on, but it has never been a problem as far as keeping pressure when the car runs.

 

What happens to the pressure at WOT/max engine load/RPM?

 

It doesn't seem to do it at WOT. The AFR is fine too. I just got to thinking that it could be because the sender for my gauge is behind my fuel solenoid for the nitrous.