I have an 89' Camaro with a 406, miniram, 30# SVO's, etc. I am running a Walbro 255 LPH intank, replacing the previous 255 Walbro. I am losing fuel pressure from 50 PSI to 44 PSI at WOT. This is with the Vacuum line undone and pressure set to 50 psi at idle no vacuum. It had the same problem with the other pump so I thought it may have been a pump going out. Fuel filter is new. Does anyone have any ideas or can testify to the lines being able to hold up to alot of volume?

Also tried additional T-rex inline and problem still exists. (Voltage good at both pumps)

 

Who did the programming on the chip?
Do you have a scanner to check what the injectors are doing?

 

Injectors are 30# at 75% Duty Cycle at WOT.
Chip is Ed wright.

 

What leads you to believe there is a problem? Does the fuel pressure regulator hold pressure after shutdown? It could be that the engine is using that fuel and so the pressure drops?

 

Built a setup almost exactly like that- 400, Miniram, dual electric pumps. On mine, however, I left the stock in-tank pump in place and used it basically just to push fuel up to a T-rex in-line that we actually mounted ON THE DRIVER'S INNER FENDER!

So, it was a bit of a rig job- certainly not as robust as your setup but it always held constant fuel pressure, putting just over 400 HP to the rear wheels. So, I think you got a problem there somewhere- you're almost certainly not outrunning the pumps unless the voltage is dropping off or you have a restriction in the line somewhere (kinked, partially blocked?).

I'm wondering if the regulator or the return line is bad. If the regulator or return line are being maxed-out you will see higher fuel pressures at idle and then they'll fall off when you go to WOT/high RPMs (where much less fuel is going through the regulator/return line becuase it's going into the engine).

See where I'm going with this? Make sense?