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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Duel tank selector switch
