FUEL PUMP ALWAYS ON

Mcmahst · Jul 2, 2026

What I like about this forum the most is I didn’t know Jack about this model years fuel pump system. The prior model years didn’t have any kind of controller for the fuel pump. It was pump on or pump off from the ECU ground. So I had to do research and dig around to try to figure out if there was any answers out there that could help you, and I’ve learned quite a bit. So again it’s why I like this forum lol.

Scwhitten · Jul 2, 2026

Mcmahst said:
What I like about this forum the most is I didn’t know Jack about this model years fuel pump system. The prior model years didn’t have any kind of controller for the fuel pump. It was pump on or pump off from the ECU ground. So I had to do research and dig around to try to figure out if there was any answers out there that could help you, and I’ve learned quite a bit. So again it’s why I like this forum lol.

Yeah this is a great forum. So I put some gas in the tank. The fuel low light went out and the needle reflected a 1/4 tank of gas. So I know that the sender side of the pump is working. But the pump still stayed on after three seconds, and just stayed on. So I swapped out the pressure sensor (that’s on the fuel rail) but that didn’t change anything. So I’m still at pump always on when key is turned. Will it ever end?

manicmechanic007 · Jul 2, 2026

Generally, when the fuel pump stays running, you need to check the capacitors in your processor
When those caps leak electrolyte, they affect the fuel pump circuit first
Zoom in the caps in this photo, and you can barely see one of mine leaking (blue capacitor top left)

Scwhitten · Jul 2, 2026

manicmechanic007 said:
Generally, when the fuel pump stays running, you need to check the capacitors in your processor
When those caps leak electrolyte, they affect the fuel pump circuit first
Zoom in the caps in this photo, and you can barely see one of mine leaking (blue capacitor top left)

Thank you, what is the name of the processor that you’re referring to?

Mcmahst · Friday at 9:12 AM

Some more stuff to read. Might help:

Fuel Systems — 2001 Ford Mustang GT V8-4.6L SOHC VIN X Service Manual | Operation CHARM

Detailed repair manual for the 2001 Ford Mustang GT V8-4.6L SOHC VIN X.

charm.li

manicmechanic007 · Friday at 5:58 PM

It's just your ECU or ECM whatever you choose to call it
Over the years they have changed the terminology enough that most techs just call it a processor these days
My 94 van has basically the same processor as all of your Mustangs (it's a A9L or something like that)
Either way, your caps are shot if the pumps stay running
** Hope they did not destroy the traces on the circuit board
My processor pictured above just barely had the problem and was in good shape trace wise

Mcmahst · Saturday at 12:07 AM

It could very well be the ECU, but with this model year, he’s got that fuel pump control module which could also be the culprit. Is there a test procedure for the fuel pump module? Does someone have a Mitchell’s book with the test procedure for this component?

manicmechanic007 · Saturday at 7:57 AM

The PCM controls the fuel pump driver module
If the driver module fails, you get no fuel pump, not constant fuel pump power

FUEL PUMP ALWAYS ON

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Fuel Systems — 2001 Ford Mustang GT V8-4.6L SOHC VIN X Service Manual | Operation CHARM

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