Fuel Pump has no Power.

TheSlowLX said:

I turned on my car yesterday and reversed down my driveway. Car dies and wont turn back on. I noticed that the fuel pump was not turning on as I turned the key. I checked and replaced all relays, check fuses, and fusible links. So I thought maybe its the fuel pump itself. I get a jumper wire and get a 12v power directly to the fuel pump. Fuel pump starts working, yet car will not turn on. And without the jumper wire, fuel pump wont come on at all. What can it be? Need Help ASAP.

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is it possible that u missed replacing the fuel pump relay? Why would u have replace all relays unless you weren't sure of which was for the pump?

TheSlowLX said:

When I ment that I " checked and replaced all relays", I was reffering to the fuel relays themselves. A friend of mine told me that there was one underneath the passenger seat, and another one on the passenger side of the fender. I found no relay under my seat, but I found it where my computer is at. It did click everytime I would turn the key, but I still went ahead and replaced it. I also replaced the other relay thats on the fender.

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There are most likely two relays on passenger side by maf. One is for a/c WOT cut-off and the other for your fuel pump. Did you check to see if for some reason the inertia switch in the hatch had been tripped?

The relay at the computer is the EEC relay. And the FP relay is either under the driver seat or on the pass strut tower (the switch was made in later aero foxes).

Good luck.

TheSlowLX said:

I get a jumper wire and get a 12v power directly to the fuel pump. Fuel pump starts working, yet car will not turn on. And without the jumper wire, fuel pump wont come on at all. What can it be? Need Help ASAP.

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Does this mean when FP is jumped to a 12v source the pump primes and continues running but the car still wont start?

Get a multi-meter and check both sides of the fuel pump harness connector by the tank. See if you have power coming into that connector and then see if you have power on the other side. My connector went bad and caused my fuel pump to go in and out while driving

You are really going to have to multi meter everything to diagnose it. I would start at the fuse block and work my way back to see if there is power on down the line. Good luck.

TheSlowLX said:

Yes, pump will continue running but the car will not start, just keeps on turning. But once the 12v jump is taking off, FP does not come on at all. I checked the EEC relay with a test lamp, light comes on. Also checked the FP Relay by the MAF and also has power. Yet no power is running to the pump.

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where are you getting the 12V source from? Reason I ask is that you may be using a 12v source that cuts out (doesn't recieve voltage) when car is actually cranking. Therefore pump is not actually pumping because there is no voltage to it during cranking.

If that's not the case then it sounds like you have two problems I would think.

Fuel Pump Troubleshooting for 91-93 Mustangs

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 5-20 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. See http://www.mustangworks.com/articles/electronics/eec-iv_codes.html for a description of the test connector. If the relay & inertia switch are OK, you will have power to the pump. Check fuel pressure – remove the cap from the Schrader valve behind the alternator and depress the core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

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 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 relay coil and then from the relay coil to the computer (light blue\orange 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 (pink/black wire) goes to the fuel pump relay contacts. When the contacts close because the relay energizes, the power flows through the pink/black wire to the contacts and through the dark green\yellow wire to the inertia switch. The other side of the inertia switch with the brown\pink wire joins the pink/black wire that connects to the fuel pump. The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays or injectors, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

diagram of the wiring for 91-93 cars.

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

Power circuits:
Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow 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.

Inertia switch: Check the brown/pink 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 dark green\yellow (inertia switch input) and brown/pink wire (inertia switch output). Power on the dark green\yellow wire and not on the brown/pink wire means the inertia switch is open. Press on the red plunger to reset it to the closed position. Sometimes the inertia switch will be intermittent or will not pass full power. Be sure that there is 12 volts on both sides of the switch with the pump running and that the voltage drop measured across the switch is less than .75 volts.

Control circuits:

Relay: The red wire for the fuel pump relay coil gets its power feed from the ECC relay. No 12 volts here, and the ECC relay has failed or there is bad wiring or bad connections coming from it. The ECC relay is located on top of the computer, which is under the passenger’s side kick panel. It is not easy to get to, you must have small hands or pull the passenger side dash speaker out to access it.

Relay: The light blue/orange wire provides a ground path for the relay power. With the test connector jumpered according to the previous instructions, there should be less than .75 volts. Use a test lamp with one side connected to battery power and the other side to the light blue/orange wire on the fuel pump relay. 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. Remove the test jumper from the ECC test connector. 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.

Computer: If you got this far and everything else checked out good, the computer is suspect .Remove the test jumper from the ECC test connector located under the hood . Remove the plastic cover over the computer wiring, but leave the computer wiring connector plugged into the computer. With the ignition switch in the run position, connect a test lamp to the battery and back probe pin 22, the light blue/orange wire with it. The lamp should glow brightly. No glow and the computer has died a sad death. If you used a voltmeter instead of a test lamp, you should see battery voltage, whatever that may be…

Fuel pump runs continuously: The light blue/orange wire has shorted to ground. Disconnect the computer and use an ohmmeter to check out the resistance between the light blue/orange wire and ground. You should see more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t jumpered to ground.

I looked the ground over by the battery (just to make sure I was looking at the black cylinder, it is the one that pulls apart in the middle by squeezing the clip,right) and it looks fine. I ohmed from ground to the other side of the cylinder and it read 2.2. Is that too high?

Could the fuel tank ground be the problem? Where is it located?

Thank you very much for your info

Back from the dead... Are you the original poster on a different name, having the same issue, or offering a suggestion on how to fix the problem? If the latter, I'm sure it was solved in November of 2005 when this thread was posted in last...

tunedin302 said:

Get a multi-meter and check both sides of the fuel pump harness connector by the tank. See if you have power coming into that connector and then see if you have power on the other side. My connector went bad and caused my fuel pump to go in and out while driving

You are really going to have to multi meter everything to diagnose it. I would start at the fuse block and work my way back to see if there is power on down the line. Good luck.

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when we check with multimeters we have to check for amps correct?

You should be checking for volts when using the multimeter.

tunedin302 said:

Get a multi-meter and check both sides of the fuel pump harness connector by the tank. See if you have power coming into that connector and then see if you have power on the other side. My connector went bad and caused my fuel pump to go in and out while driving

You are really going to have to multi meter everything to diagnose it. I would start at the fuse block and work my way back to see if there is power on down the line. Good luck.

Click to expand...

A picture may help...