cannot switch fuel tanks

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Aug 11, 2015 | 12:20 AM

joedirt1971

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cannot switch fuel tanks

i have a 1995 f350 xlt gas 7.5l 4x4 crew cab with auto trans. i am having a problem switching tanks. i foolowed your advice subford as on other posts and found a problem with the inertia getting power. that bieng solve it will now pump but i get no fuel to fire the engine. previously i had no powewr to tank switch but i have temporarly jumped it to figure out the problem.the guy i got it from said the front tank never worked. so i got a new spectra fuel pump n hanger the complete assembly. boom no prob right? thats when i started reading on it and found the prob at the relay. that bieng said do i have a tank selector and if so any pics? ive followed the fuel lines and see nothing. did they bypass it? thanks

Aug 11, 2015 | 08:19 AM

rla2005

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Your truck does not have a Dual Function Reservoir. Ford stopped using those in the 1990 model year gas engine trucks. Did you trace out the power from the dash mounted selector switch to the tank using a test light? Using a high impedance DVM will result in chasing phantom voltages.

Aug 11, 2015 | 08:18 PM

joedirt1971

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thanks for thr reply rla2005. i have no power at the fuel pump relay going to inertia switch. i remove the relay and jump the wire i get power but no start. i hit the black wire with thr red stripe with the test light n relay activates. you can hear it clicking.

Aug 12, 2015 | 06:48 AM

rla2005

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Quote:

Originally Posted by joedirt1971

Not sure which wire you are referring to (Circuit is the same for a 7.5L):

Further downstream:

Aug 12, 2015 | 07:14 PM

joedirt1971

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after putting glasses on i see it is the lb\o wire on the fuel pump relay that makes the clicking sound when i hit it with the stab light

Aug 12, 2015 | 10:15 PM

joedirt1971

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do i need a new computer for the truck? should it be providing aground?

Aug 13, 2015 | 10:30 AM

rla2005

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Quote:

Originally Posted by joedirt1971

do i need a new computer for the truck? should it be providing aground?

That means the command from the computer to energize the Fuel Pump relay is either not getting there or is not commanded. This can be caused by an open wire or poor connection from the computer to the relay socket for the former scenario or a bad computer for the latter.

I would verify the signal is leaving the computer by checking the output on Pin 22. When you cycle the key from Off to Run the computer will ground the relay, energized state, for ~ 1 second then drop out. If you have that then you know is a wiring issue. If not, you have a bad computer. Highly suggest you pull the computer (PCM) and inspect for signs of leaking capacitors. A very common issue on these trucks.