Fuel Pump Orlando guys come in.

Fuel Pump Troubleshooting for 87-90 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 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/black wire) then from the inertia switch to the relay coil and then from the relay coil to the computer (tan/ Lt 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.

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 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, bad ignition switch or ignition switch wiring or connections. There is a mystery connector somewhere under the driver’s side kick panel, 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 all of the checks have worked OK to this point, then the computer is bad. The computers are very reliable and not prone to failure unless there has been significant electrical trauma to the car. Things like lightning strikes and putting the battery in backwards or connecting jumper cables backwards are about the only thing that kills the computer.

Can't help ya tonight but I can probably give ya a hand tomorrow after I get off work. I am usually out of work by around 4pm. I'll pm ya my cell # and give me a call if you haven't gotten anyone else to give you a hand.

That is cool. Stangers helping one another out, hands on. Its a good idea to have a filler neck grommet on hand when you pull the tank. They are pricey at $20 or so at your local ford or mercury dealer. Call first, ford didnt help me, mercury did. I was lucky I had that part on hand, you can always return it if you dont need it. I recommend replacing it if its old, unless you like fuel leaks.

The mustang is by far one of the easiest tanks to remove. Piece of cake.

Here are some useful tips...

I have done the tank removal twice, and the main issues are getting the car up on jack stands and getting the gas out of the tank. DO NOT try to do this job without jack stands. Becoming a pancake is not part of the repair process.

Some 5 gallon paint pails lined with garbage bags are good to hold the gas. The garbage bags provide a clean liner for the pails and keep the loose trash out of the gas so you can reuse it. A piece of 1/2" garden hose stuck down the filler neck will siphon all but a gallon or so of the gas.

Remove the filler neck bolts and put them in a zip bag. Disconnect the supply & return lines by removing the plastic clips from the metal tubing. If you damage the clips you can use tie-wraps as a substitute when you re-assemble them. Then you remove the two 9/16" nuts that hold the T bolts to the straps. Put the nuts in the zip bag with the filler bolts. Pull the plastic shield down and away from the tank. Once the tank drops a little bit you can disconnect the wiring for the pump & fuel quantity sender.

The pump assembly comes out by removing a large metal ring that unscrews from the tank. You are supposed to use a brass punch to tap on the ring so that you don't make sparks. Look closely at the rubber O ring gasket when you remove the sender. The pump assembly requires some twisting and turning to get it out the hole.

Look very closely at the electrical wiring. The stock wiring can overheat and melt the insulation. Mine had some really crummy plastic tubing slid over the quick disconnects. If the wires ever got together, there would be sparks inside the fuel tank and no more Mustang. I eliminated the splice in the middle of the wiring and went straight from the pump to the feed through connectors for the wiring. It required some soldering and crimping of new tabs on the wires, but it made a neater job.

Inspect the pump mount to metal tubing bracket. Mine broke and I couldn't get it to solder back together. I drilled a small hole for a machine screw & self locking nut to hold the clamp and bracket together.

The pump is easy to get off the mount but is somewhat difficult to get back it the tank without damaging the sock filter or tearing it on the tank baffle. When you install the metal ring that holds the pump in place, watch out for the gasket O ring. Some RTV may be helpful if the ring is not in excellent condition.

I used a floor jack to help lift the tank back in place. You may find that it is the only time you really can make good use of a helper.

If you have to move the car in a pinch, if you knock a few times on the top of the fuel pump assembly, basically where the plastic ring tightens, with a screwdriver or something, it sometimes kicks on. At least in my experience it did. If you don't find someone to help you by Thurs, I can help you out too. PM me Wednesday if you need me.

Yep, ideally if you can get it to start one last time, we could do it in my garage where I have many fun and air powered tools, not that we really would need them in this case.

The ring that holds the pump mount plate has some prongs that stick up, kind of like a crown. You use a brass punch on the prongs and tap it counterclockwire to loosen the ring.

Examine the O ring gasket under the plate to make sure it is in good shape before re-assembling it. A little grease on the O ring gasket and other parts will help it go back together easier.

Best way to get it off is with an oil filter removal tool. The ones that are shaped like giant pliars, you know what I mean, work like a charm.

hey if u need help i could help you... i have droped my tank three times! so i got sick of it and replaced everything from the tank to fuel pump! so if u need a hand give me a IM and i will help ya out if! i can do a fuel pump in under 45mins including droping the tank!