possible fuel pump problems

[no_ftchx]

Alright here's the deal: i turn the key to the start position and everything turns on normally, i then let off and let the it go to the run position and the car dies. The fuel pump will run when the ignition is in the start position, but not when it's in the run position. Not long ago i was about to take the car out and i didn't even make it out of the driveway when the battery shorted out. The battery is mounted in the rear and the pos. and neg. cables had melted through their insulation and were laying on top of each other. I don't know if that short could have tripped or blown something but i could use any suggestions right now. Thanks.

 

[HO93LX302]

Ok so when you turn the key on you can hear the pump prime?? and when you start the car it just dies?? have you checked fuel pressure at all?? If not do that and see what it says.. Its possible you need a new fuel pump

 

[90mustangGT]

Have you checked fuel pressure? What does it read?

 

[no_ftchx]

when i turn the key to on i don't hear the pump at all, i'll turn the key to start and the pump will come on and the engine will start, but then i'll let the key go back to run and the pump will stop and the car will die.

 

[no_ftchx]

it was running good not even 45 minutes before. before the battery shorted out

 

[HISSIN50]

ignition switch wiring? not getting continuity in the run position. you can jump the relay or the self test connector to run the pump to rule out other things. as i recall, the puter sends the relay a ground pulse.

it runs, apparently has pressure at some point, and the lack of priming in run position points to continuity issues to me.

good luck.

 

[jrichker]

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect for fuel escaping while pump is running.

The electrical circuit for the fuel pump has two paths, a control path and a power path.

The control path consists of the inertia switch, the computer, and the fuel pump relay coil. It turns the fuel pump relay on or off under computer control. The switched power (red wire) from the ECC relay goes to the inertia switch (red wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (green wire). The computer provides the ground path to complete the circuit. This ground causes the relay coil to energize and close the contacts for the power path. Keep in mind that you can have voltage to all the right places, but the computer must provide a ground. If there is no ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like fuses, except they are pieces of wire and are made right into the wiring harness. The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the contacts to the fuel pump (light pink/black wire). The fuel pump has a black wire that supplies the ground to complete the circuit.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)

http://www.veryuseful.com/mustang/t...witchWiring.gif

http://www.veryuseful.com/mustang/t...inks-ign-ac.gif

http://www.veryuseful.com/mustang/t...91eecPinout.gif

Now that you have the theory of how it works, it’s time to go digging.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring or connections. There is a mystery connector (one I haven’t found) under the dash somewhere, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously described. Look for 12 volts at the Light Pink/Black wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed or there is a broken wire in the relay control circuit.
Check the Red/black wire, it should have 12 volts. No 12 volts there, either the inertia switch is open or has no power to it. Check both sides of the inertia switch: there should be power on the Red wire and Red/Black wire. Power on the Red wire and not on the Red/Black wire means the inertia switch is open.

The Tan/Lt Green wire provides a ground path for the relay power. With the test connector jumpered to ground, there should be less than .75 volts. Use a test lamp with one side connected to battery power and the other side to the Tan/Lt Green wire. The test light should glow brightly. No glow and you have a broken wire or bad connection between the test connector and the relay. To test the wiring from the computer, remove the passenger side kick panel and disconnect the computer connector. It has a 10 MM bolt that holds it in place. With the test lamp connected to power, jumper pin 22 to ground and the test lamp should glow. No glow and the wiring between the computer and the fuel pump relay is bad.

If and only if you have followed the test procedure to this point and still haven’t found the problem, the computer is suspect :