1987 mustang fuel pump issues.

eddeyeskull · Jan 8, 2023

Car: 1987 GT 5.0 speed density motor
My fuel pump won't shut off when I turn the car on. And if I don't start the car fast enough, fuel will start shooting out some injectors.

I've replaced:
Fuel pump relay
ECM/ECU ( and it is grounded solid )
Fuel pressure regulator
Injectors

Nothing online I've read has the same problem where the pump is forcing fuel out the injectors. I've cleaned and put new injectors in and they held back the pressure for a moment and then it got forced out again. I'm at a loss.

Noobz347 · Jan 8, 2023

Post up a pic of your engine bay to include the BAP sensor that's up against the firewall.

TimC · Jan 9, 2023

I'm no expert but perhaps a bit more info would be helpful.
1) Is this a new issue?
2) what things have been recently changed or modified before this became an issue?
3) Are you rescuing a car that someone else gave up on (LOL)?

If this has been your daily driver for awhile, that's one thing. If this is a new project to you....that is a different matter.

Lots of experienced guys here. We can help you sort it out.

A couple of suggestions to get you going:

1) Look at the diagnostic port/plug hidden by the brake booster. Perhaps someone has left a fuel pump jumper wire in there.
2) Perhaps a PO has hard wired the fuel pump to an ignition source, by passing the factory wiring. Have you downloaded a wiring diagram for the car, and compared the diagram how your fuel pump on your car is ACTUALLY wired? There is a real good fuel pump diagnostic checklist on this site. Try a search for it, and follow it, step by step, focusing on the continuous running issue.

Mustang5L5 · Jan 9, 2023

Go back to the fuel pump relay.

I only have the '88 EVTM handy , but '87 might be the same. You have 4 wires at the relay

Orange/Light blue : FUel pump source power (you should have power here)
Pink/Black: power out to fuel pump (power here when relay is closed)
Tan/Light green: Relay ground to ECU pin 22 (this is the grounding trigger for the fuel pump. Ecu grounds this pin and that activates relay)
Red/Black: 12V from inertia switch to power the relay coil (key on power)

Test continuity from the tan/light green to vehicle ground. See if it rings out constantly. Do it at the fuel pump relay plug, and if it does, i would disconnect the ecu and try it there. That pin 22 triggers everything so the question is if it incorrectly on all the time? That would point to an ECU fault.

A constantly running fuel pump is a classic symptom of a failed capacitor on the ECU. You might want to pull the ecu out and open it and inspect the capacitors. However a visual isn't always the best way, as i replaced some caps in a ECU that looked great, but one was failed. Visially it looked new

1987 mustang fuel pump issues.

eddeyeskull

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Noobz347

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TimC

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Mustang5L5

That is…until I whipped out my Bissell

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1987 mustang fuel pump issues.

eddeyeskull

New Member

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

TimC

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Mustang5L5

That is…until I whipped out my Bissell

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