I bought a 87 F150 4x4 last year and it sat all winter. when i had bought it fuel gage was not working, selector switch did not move when switching tanks, but motor never flinched while running. No matter the position of the selector would only run on the midship tank. Is this a inherient problem withthe ford. all fuel lines are in tact and look to be all original. How do I test the selector valve to see if it works? or wiring ? I started the truck and played with selector switch and eventually unplugging it from the harness hoping it would stall the truck. it had no effect. what is wrong with my truck?

 

Maybe a bad switch, wiring and plugs, hose in the tank or a bad pump.
Could be a bad valve but check the other things first.

When you turn the ignition key to on and not start the engine, the fuel pump on the frame rail and the selected in tank pump should run for about 1 seconds.

By grounding pin #6 of your self-test (DLC/VIP) connector with the key on you should get fuel pressure at the fuel rail (manifold) schrader valve should be around 42-45 psi if you have an V-8 and 55-60 psi for a six.

To trouble shoot the pumps that are in the tanks you need to unplug the electrical connector to the frame mounted pump so you don't continue to run the pump dry while you trouble shoot the in tank pump.

To verify the in tank pump is working, disconnect the supply hose going to the back of the selector valve.

On the back of the tank selector valve are 4 ports. Two from each tank.
The larger diameter hose is the supply hose the smaller hose is the return hose.

If you have full tanks the fuel will flow out of the supply lines from the tanks without the pumps even running but with pin #6 grounded of your test (DLC/VIP) connector and using the old style fuel pressure vacuum gauge you should get around 5 PSI fuel pressure from the selected tank.

So if you trace the larger diameter hose from the tank you're working on, place the end of the hose in a bucket turn on the key with pin #6 grounded of your test (DLC/VIP) connector grounded you should see fuel being pumped out of that tank. About 16 oz in 10 seconds.

If these tests looks good, reinstall the hoses and disconnect the hose at the input of the frame rail mounted fuel pump. Do the same test. If no fuel comes out of the hose, the selector valve is probably bad.

Only the Ford dealer sells the proper tank selector valve.
Part # F1UZ-9b263-B It's called a Fuel System Service Kit.
Should cost around $77.00.

The selector valve may be full of junk and not letting the fuel through it also but if it runs on one tank it and not on the other then it would sound like the other tank has a bad fuel pump.

How the valve works is:
There is a lock on the center rod inside the selector valve that locks the valve to a tank and a diaphragm in the top of the selector valve to move the center rod to lock it to the other tank. Fuel pressure from the pump in the tank is sent to the top side or the under side of the diaphragm to snap it to the other tank that is selected by the tank pumps.

There is a plate attached to the diaphragm and the center rod that is also attached to two more rods that go to two valves that decide what tank the fuel is coming from going to the engine and what tank the return fuel is going back to.

For more information on the valve go to:
http://www.stangler.com/motorsports/...alve/index.htm


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I will test your ideas as soon as the weather breaks. Does the relay operate both intank fuel pumps? Is there a second relay for the back pump? Main tank is full, unknown of age of gas, at least 1 year that i had the truck. Is it possible all is working correclty but selctor valve is stuck in the midship position?

 

Yes it operates all three pumps. The two in the tanks and the one on the frame.
No there is not.
Maybe but more than likely the rear pump is bad or the hose in the tank has dissolved.

 

i worked on an 89 for someone. their trucks sending units would peg overfull and only run on one tank no matter the position of the switch. i found a fuse that operates the selector valve or something like that once i put that in the sending units work and it switches tanks. it's a 10a fuse in position 15.

 

Fuse position 15 is blank and not used in a gas truck.
Position 15 is for the motorized fuel selector motor on Diesel trucks only.
There are no fuses for the selector valve as there are no wires going to the selector valve.

 

I much appreciate all input and want to say thank you for responding to my questions.