RE: 94' Explorer fuel pump voltage
Has anyone checked or replaced the fuel pump relay out in the battery junction box?
Fairly common failure for pump intermittents, and certainly one of the places I'd look first, but not the only cause.. The way the system works in general forpower distribution is this,,when the key is cycled 'ON' the PCM (vehicle's computer) will activate the fuel pump relay (in the battery junction box under the hood) for only a few seconds to pressurize the fuel system by running the pump for the startup.. The voltage from the'closed fuel relay contacts' flows to/through the inertia fuel cut off switch and finally down to the fuel pump.. If the engine is cranked,, the pump will be activated as well, but unless the PCM detect's an RPMthe pump won't continue to run, or if the inertia switch opens the circuit in a collision ect.. If the PCM commands the fuel relay to close and it's failed,, the current won't run down to the pump or may be intermittent pump run times.. The fuel pump relay connection/plug is also an easy way/place to test run the pump by bridging theremoved fuel relay connections and manually completing (adding voltage) the voltage circuitdown to the pump, taking the fuel pump relay and PCM's control out of the diagnostic loop, as well as to test therefor applied/available voltages fom the fuse panel.. On a vehicle with a failing pump, sometimes you'll have luck holding the key in 'either' the ON position (or crank the engine) and have someone 'bang' the bottom (forward area) of the fuel tank.. Sometime the 'jar' will start the pump up, and if so, usually will condemn the in tank pump unit.. If the PCM was at fault for not closing the fuel pump relay, you can either remove the relay and bridge the power/pump connection as before, or even add a temporary ground (PCM controls the ground) and the relay (if good) should close allowing the current to flow and run the pump.. Although the relay/PCM control should bein good orderforsafety reason....
If there's 12v voltage through the inertia cut off switch, then the next place to check would be on down at the fuel pump/module connector as well as all grounds.....
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