Need help with fuel pump!

Don, i would get to the FP relay and check each terminal's output. that gives you a direction to go, to find the problem.
Tom's diagram might help out. good luck.

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

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/article...c-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.

See http://www.autozone.com/images/cds/...23d80195960.gif for a diagram of the wiring for 90-93 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 less than 1 volt.

Fairlane said:

anyway, i still have no power coming out of the relay under the seat. There is power going in but none going out when the key is engaged.

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right, i kinda figured that. grab your DMM and check what each terminal is reads. what im saying is in line with what JR is saying as well.

you will have constant juice to the relay socket. when switched, the output, and the relay coil positive trigger will have 12 volts when priming/running. the puter supplies ground for the neg relay coil, as i recall. see what you have - the EEC relay would likely keep the ground coil from showing up. again, Tom's or autozone's schematics can illustrate what im saying. look for the FP relay in either diagram.

this is how i would do it anyhow - depending upon what terminal on the FP relay is missing what it should have, that tells you which way to look. im not a whiz like JR, so i thought saying it this way might make more sense (how it makes sense to me - though lacking the thoughtfulness and thoroughness of JR's post).

Fairlane said:

ok, now i have replaced both of the relays just to make sure that is not the problem. Is there a fuse somewhere that i need to know about and check? I see some fuses on the diagram, but i don't know where they are. Does anyone know where they are located? thanks -don

Where are the grounds located for all of this wiring to the fuel pump. That's almost what it has to be. Maybe i knocked one lose when i was droping the fuel pump.

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Don, i dont know how much more info JR can give - his write up is pretty explicit. there is a fusible link off the starter solenoid - i dont know of any other fuses or fusible links in the circuit. the fusible link is Or/lt blue on earlier cars - i dont know about yours. check it for signs of having burned through. also probe each side of it to ensure continuity - it is hot at all times. or if the Or/lt blue wire, at the FP relay socket, is hot, chances are it is ok (although Fusible links have burned enough to show voltage, but flow hardly any amps.

good luck.

You can do two things: guess at the problem, throw parts at it and be frustrated because it is hard to fix.

OR you can go back and read the test path, print the write up and the diagrams. Sit down and draw the electrical power flow through the circuit on the printout of the diagrams.

Think about two things: you have to have power and you have to have ground. If you are missing either one, the circuit will not work. Look at the diagram: where does the power come from? Look at the diagram again, where does the ground come from?

There are two circuits in the fuel pump system. There is a power system and a control system. Each one has its own separate power and ground path. Trace the path from power to ground in each system to understand how they work and how to troubleshoot them. If you will discipline yourself to do this, the problem will not be hard to diagnose. Once you have the correct diagnosis, the problem will be simpler to fix.

Something simple to check...Maybe take a look at the automatic shut-off switch, see if the red button is popped out.

PNY PWR said:

Something simple to check...Maybe take a look at the automatic shut-off switch, see if the red button is popped out.

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Don, he is referring to the inertia switch. JR's long post has a paragraph about it - look for the paragraph beginning 'inertia switch'.

the switch is behind a cover in the trunk/hatch area.

good luck.

sorry, I didn't read all the other posts compltely.

PNY PWR said:

sorry, I didn't read all the other posts compltely.

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oh no, you are cool. it was a good suggestion (one that i would have reiterated). JR's lists are great, but one can get lost pretty easily. i only said what i did in the last post so Don would know what you were talking about, in terms used by JR in his master list.
(JR does not list an 'automatic shut-off switch' )