Fuel Pressure Drop After Pump Turns Off
 

have a 2003 Silverado SS with a 414 I just swapped in and I'm having problems getting it tuned. The AFR keeps fluctuating at WOT. Although I think I just narrowed the problem down.

I'm running the stock fuel pump, with a Walbro Inline pump. It then goes up to an adjustable fuel pressure regulator which feeds the rails and sends the excess fuel back to the tank. When I turn the key on, the fuel pressure goes up to 58 psi (where its set at) and then quickly drops pressure as soon as the pump turns off. It will drop down to 10psi fairly quickly, then after another 10 seconds or so drops down to 0psi. Is this normal for an '03 Return style fuel system? As far as I understood it should hold pressure when the key if off, so I'm assuming either a bad check valve in the pump or a split in the fuel line in the tank. I cannot find fuel leaking from anywhere else.

it should hold pressure, the injectors could be leaking or the regulator could be bad also.

I took the return hose off the regulator, and as soon as the pump shuts off, the return on the regulator quit draining fuel. I assume this means that it is leaking out of the injectors, the check valve is bad, or a fuel line split inside of the tank.

But this is assuming that the system SHOULD hold pressure when the pump turns off. Every other vehicle I have access to right now is a returnless style system but they all hold pressure when the pump turns off.

Any fuel in the vac line that connects to the regulator? It should be dry.

There is currently no vac line hooked up to the regulator. I have the vac port capped, but, there is no fuel coming out of the vac port. I checked it to make sure it was dry.

I have heard of the little plastic hose that goes from the pump to the top of the pump module, getting a pinhole in it, I would imagine that would allow fuel to drain back into the tank pretty quickly...

Yea, I've been reading that here and at silveradoss.com

I'll be pulling the tank tomorrow and checking it.

I know I commented on the other site however my current set-up (similar to yours) does drop pressure after the pumps are cut off. I see this after the "key on",...the FP will go to about 58 (where I set it) and after the 3 second "prime" when the pumps kick off, my FP will drop. This same observation was noted on my old Radix/6.0L combo.

Maybe I have had an issue for 3 years and never noticed it.

I was able to get a fuel guage hooked straight to the stock fuel line. The stock fuel line holds pressure no problem. It started at 150 psi, fell to 125psi in about 15 minutes, and overnight its still at 75psi.

Also found that its the regulator leaking fuel through to the return line also. I've got a new Aeromotive regulator coming in today to replace the Professional Products regulator that was on the truck.

Where is your fuel pressure gauge and fuel regulator located on your system. if it is located after the regulator then you will drop pressure after the pump is cut off. If before the regulator which would make no sense then it would hold pressure as long as your check valve is good.