Hey gang... first of all great website, VERY helpful! Here's my problem.... 1988 E-250 5.8L dual tanks, I can get the fuel pressure up to 40 psi in the rail after turning the key on and off several times. Start engine, pressure drops slowly, and in about 10 seconds or so, pressure drops to 10 psi or so, and engine stalls. I replaced the fuel pressure regulator, same problem, replaced the fuel filter, same problem. High pressure pump runs, but sounds noisy. Last night I disconnected the fuel line from the front of the tank switcher/canister,the one that feeds the high pressure pump, and turned on the key, high pressure pump runs for 1-2 seconds, like it's supposed to, but no fuel pouring out from the disconnected line at the canister. It does this is both fuel tank positions on the switch, and the fuel guage reads correctly for both tanks, (at least one shows a 1/4, and the rear shows 3/4, which I think is about right) Wouldn't the pumps in the tank run? Could both pumps fail at the same time? Is there a seperate electrical supply for the in-tank pumps from the high-pressure? I have a Haynes manual, and it doesn't give much info. I also do not have an owners manual for fuse locations, etc., although all fuses tested OK the other day. Thanks in advance for any help!

 

I have a Fseries manual sooo I hope the basic info is the same. I am not going to give wire colors since don't know if they coincide. The hi-press pump gets it's voltage from the same source as the in-tank pumps so would say fuses, relay, inertia switch are fine. The dash switch routes power to the proper in-tank pump thru two about 12 gauge wires. I would pull the switch and check for power out on each of those wires. The gauge is run thru separate wires, so it could still function even if the pump circuits went bad. Possible that both pumps failed at the same time, but not likely.