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1992 F250 7.5L/460CI - No Fuel Pressure Rear Tank Fuel Pump
Problem - No pressure from rear fuel tank fuel pump and no audible sound from pump when energized.
Note: Front fuel tank leaks and is not used.
Fuel Pump Fuse is good with 12 Volts going to it. Fuel Pump Relay has 12 Volts. Inertia switch not tripped
Removed old pump and cleaned inside of tank thoroughly.
Installed new fuel pump in tank.
Serviced with gas. When ignition switch is engaged I hear the rear fuel pump run briefly but there is no pressure or fuel coming from the pump. Not even with the fuel lines disconnected. Could pump be running in reverse?
Fuel pump harness to fuel pump (original) wire colors:
Orange – (Pump ground)
Brown with white stripe – (Pump power) approximately 7.5 Volts
Yellow with blue stripe - (Gauge power) approximately 7.5 Volts
Black - (Gauge ground)
New fuel pump wire colors: I am not sure about the function of the wires on the new fuel pump, no wiring diagram to be found and I failed to see where they are connected to the pump before installing it.
Black – (Pump ground?) * Connected to Orange – (Pump ground)
Gray – (Pump power?) * Connected to Brown with white stripe – (Pump power)
Purple – (Gauge power?) * Connected to Yellow with blue stripe
Black with white stripe – (Gauge ground?) * Connected to Black
Thanks in advance for your inputs.
Last edited by Tenn; Nov 3, 2019 at 01:32 PM.
Reason: left out photo
What you did was replace the whole pump/sending unit.
You need to check the wire connections into the actual pump to see what polarity they are. You say didn't see the connections but there must have been a connector/sleeve on the actual pump where you could get a look at the wires.
If the wires were totally encapsulated, you could still use a meter and figure out which ones were which.
It's entirely possible you have it running backwards if the pump ground is isolated from the sender bracket it's mounted in (otherwise it'd pop the FP Fuse as soon as the power came on).
Was the connector on the new unit different from the truck and you cut and spliced?
Did you do the isolation of the front tank? If not, is it possible that now the FP is pumping to the front tank instead of past it?
Thanks for your input. I spoke with a mechanic at a Ford dealer today, bought him lunch for advice. The pump wiring is connected correctly but the voltage at the pump is too low, should be 12 volts not 7.5 volts. He said, ensure battery is fully charged, then jump from battery to "Grey" pump wire and pump should run. Test fuel relay for correct operation and look for corroded or chafed wires. He said his money is on a bad relay. I'll post back what happens.
If you did not know the power will only be at 12 (battery voltage) for one second each time the key is turned to the run position.
It may also be 12 volts for only one second when the key is turned to the start position if the PCM is not receiving a PIP train.
However it will be at full voltage as long as the engine is cranking with a PIP train going to the PCM from the distributor.
After one second the 7.5 volts is normal with a high impedance meter. That is why I like to use a bulb type (not LED) loading test light in this circuit. Do not use a meter as it will send you down the wrong path.
The 7.5 Volts is coming from the PCM Computer.
For working with and testing this circuit you need to ground pin #6 of the EEC self-test connector and turn the key to the run position.
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