A fuel tank selector valve allows the driver to switch between the two fuel tanks found in many models of Ford trucks. The selector valve is connected to a switch that is found under the driver's seat or to the right of the steering wheel in most Ford models. When the switch is flipped, a signal is sent to the selector and one of the fuel tanks is closed.
One common problem related to the fuel selector valve is one gas tank starts to malfunction, while the other appears to be working fine. Most selector valves have six valves. There are multiple fuel sending valves and return valves on the selector. If the fuel selector valve is malfunctioning, the valves do not open and close correctly. This means only one fuel tank may be accessible.
One way to fix this is to check the wiring running to the selector and the fuel selector valve switch. Check for frayed or loose wires. If this is not the problem, the small motor that opens and closes the valves in response to the switch being moved may need repair. It is also possible that the selector valves are clogged, or the fuel filter for the malfunctioning gas tank is clogged.