OK guys. Here's the deal. My FAST XFI controls the fuel pumps. I'm running dual 255 in tanks. When I turn the key on the fuel pump primes for 3 seconds FP goes to 45# then when it shuts off pressure goes to 0. If the FAST sees a RPM signal it will turn on the pump and FP rises back to 45#. I'm running parallel fuel rails with -8an supplies and two -6an return lines from the rails into a Magnafuel FPR back to the tank. All stock lines are removed and have been replaced with -8an supply and -6an return. Is this normal for my setup. I remember with the stock setup FP would stay at 43# for a while when the key was turned on. Thanks, Rob.

 

Seems to me there are really only 3 things that could affect the fuel pressure dropping.

1. Injectors being pulsed when the XFI system is being shut off, allowing the f.p. to drop or leaking injectors...not likely the case and since you have a rather large volume fuel system, it would seem likely that it would take some time for the pressure to drop to zero.

2. The f.p. regulator is not working properly, but it maintains pressure adequately when the FAST system is powered up, so it doesn't seem likely.

3. Internal check valve in one or both fuel pumps aren't holding. Do you have the dual 255's wyed together inside the tank (like most) and then the supply line splits again just before the rails? If one of the internal check valves is "leaking", it will cause the f.p. to drop to zero in a hurry.

Just a couple of quick thoughts

 

What are you using for a fuel pressure regulator? Many of the high end regulators have a feature that relieves fuel pressure on shutdown. I run a Weldon AFPR and it works that way. Pump primes, pressure hits 58psi, and then the pump shuts off and the pressure immediately starts to drop. Typically its at about 35psi by the time I hit the start button.

My MoTeC ECU has an option to pulse the injectors when the throttle is blipped, in order to put some fuel into the cylinders for cold startup. But it starts fine without it, even thought the fuel pressure starts to drop as soon as the pump(s) shut off.