I am running a 89' Camaro w/ 408,AFR heads, TPIS Miniram, 236/242 cam. etc. The problem I am having is that I will set Fuel pressure with vacuum disconnected. Set pressure to 45psi, when I do a pull driving Fuel pressure drops to 42psi. Check pressure at idle still at 45psi. Turn pressure up to 54psi at idle, do a run and drops to 50psi @ WOT with vacuum still disconnected. I figured that if I was loosing volume that I would loose more pressure at the higher FP.
What I have Tried, that has resulted in no change:
Disconnect return to check restriction. ( ran ext line for return)
Replaced Fuel pump from 255lph, to another walbro 255lph.
Changed Filter, installed T-rex inline , replaced fuel pressure regulator, Checked Pressure before the rails, Injector Duty Cycle 78%.

Any Ideas? I am looking into an Aeromotive kit then doing sumped tank. But I figured that 255lph would handle it.
Thanks, Chad

 

What size injector's ? What is the voltage at the pump under a load?

 

30# injectors, 13.3V at pump with DVOM. Thanks

 

Chode89,
I know it might sound silly, however, when I replaced my old T-Rex pump with the Walbro 255 inline, I wired the damn thing backwards (hard to tell because they aren't marked) and when I hit the gas pedal the fp would go down. Just thought I'd post up my experience. One other thing I was thinking are you running a inline along with the Walbro 255 or is it just the intank?

Cheers,
Tim

 

Nothing sounds silly, I just want to get this thing fixed. I know for sure I had it hooked up right. Ran the T-rex inline then when it did not change I took it back off(borrowed it from a friend). Thanks

 

Doesn't hurt to try reversing those wires and take her for a drive. Like I said, I felt very silly because I had the same thing happening (losing fuel pressure when hitting the throttle) and decided to swap the +/- around and presto ----- that was it. I hope it's something silly like that for you as well.

Cheers,
Tim