Culprit: 1985 E350 van chassis motorhome, 460 carbed, C6, front/drivers side 15 gallon tank, rear/centered 20 gallon tank. 6-port electric selector valve, in-tank separate electric fuel pumps, NO mechanical or external pumps. Switch under dash for tanks, relay on the driverside fenderwell.

Issue: Switched tanks from near-empty front to full rear, no fuel, motor quits. Switched back, no problem.

Initial solution: replace rear tank fuel pump, did that last night, old pump bench tested fine but never know....but no dice.

Some more tests lead me to believe that the rear pump is getting a "pulse" power but never a full circuit. My question is, what switches the electrical constant-hot from the front to the rear tank? Is this part of the 5 wires on the selector valve? Or is this part of another relay somewhere I have yet to locate?

Went thru the wires this morning for a hour and got all the wires-colors down. Switch seems to swap power correctly....4 wires there, constant hot in (red/yellow) with a rear-hot (red/yellow), a front hot (brown/orange), and a black ground wire. The switch does change current properly.

The switching valve has 5 wires, orange, green, green/red, brown/orange, and red-yellow. The rear tank has three wires, orange (power), red-black (fuel gauge), and black for ground. Front tank is brown/white (power), green-red (fuel), and black for ground.

TIA....

 

I have a 1988 E150 with a 302. Two tanks. The book I have on the VAN says I have 3 pumps. one in each tank and a high pressure one and then a selector valve. I would think that the selector valve would be at fault in your case. especially being that it works on one tank but not the other. The book I have says that when you select one of the tanks you pick up a selector relay but if you select the other pump you do not pick up the selector relay.

I just had a simular problem with mine and the problem was the Fuel pump relay up in the engine compartment. My Van would not start period no matter which tank I selected.

I think the PULSE power is the power for the fuel guage it is pulsed...