Fuel pump help

What year is your car? Your fuel pump relay is either under your drivers seat or I think under the MAF on like 92-93 or something. The one you replaced I bet is the EEC Relay. When you turn the key to the start position, the fuel pump primes, so try that and see if you hear it kick on. Are you sure your inertia switch isn't triggered? It's the button in the hatch.

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 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/tech/engine/images/IgnitionSwitchWiring.gif

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

http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.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.

Mathew, go to
www.veryuseful.com
you can scroll through and pick out what you need/want.

good luck. oh yeah, im thinking that you might have been in the area of the EEC relay (like The User said). the EEC relay is usually above the puter.

for others: there are a few threads on this whole deal. if interested, search Mathew's threads started for all of the pages of frustration. he has no juice to the inertia switch.

i think i was talkin about this in one of the last threads (that we kinda knew where the problem - if only one- was, since we knew you had no juice at your inertia switch).

that wire comes from the EEC relay, IIRC. now i have some ideas of how i would rig it (like removing the existing relay and running a new SPDT relay with the existing good wires, along the lines of simply bridging the wire from the fusible link to the line to the pump, but with a relay). with a simple bridging of the wires, you would have to pull the bridge each time you started and turned off the car.

i am no Jrichker, TMoss, or anywhere near being in their league. i would really like to hear what they say about how to go around your lack of juice from that wire. even if i rigged it, i would ask for how to re-wire/ fix it, but a rig could work short term. they are both real whizzes with the computer stuff, and would know what is safe to do and what is not.

i would just run a wire that is key-on hot for now (to a new relay) or bridge the two terminals i mention (bridge them at the relay connector). but I WOULD NOT DO THIS WITHOUT ASKING ONE OF THEM - I dont want to suggest something that could mess your ride up more. please dont act solely on what i said. this is just my thinking, for the experts to work with.

good luck.

Sorry about the bad links, they are fixed now.

The first link will enable you to put the pump in test mode, which will run continously as long as the ignition switch is in the run position.

Follow the test path and you will find your problem, there is better than 95% success rate if you have any electrical skills at all.

Jrichker is an expert, i'd say go through his steps. Otherwise, get a toggle switch and about 20 feet of wire (not sure what guage) and run the pump directly from the battery through the toggle. I have my GT this way, but I probably will put it back to normal when I actually get to drive it soon. I put my toggle in the ash tray. Find the power wire for fuel pump (don't guess it matters where you splice as long as it's the power wire, but mine is right at the fuel pump.) I hooked the other wire to the starter solonoid. Good luck.