No fuel psi at key on

+1 for the pump.

What was the fuel pressure when this happened?

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/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 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.

I know that yall are all leaning towards the fuel pump, but it sounds exactly like what my car is doing. You just might want to try to replace the MAP sensor. Sounds like the engine is flooding and /or running rich as hell. As for the list of replacement parts you listed, sounds like you got everything except for that. Try it and see if you want to.

Nate

Quit throwing parts at it until it gets fixed. This is hard on the pocket book. I don't know what a used map cost, but you can check yours with a multimeter for free. or for $3 bucks for a cheap one at Harbor freight. This is just MHO but a map sensor wouldn't prevent the pressure from rising at koeo. I highly recommend doing a test only on the system before the pressure regulator. Crimp off the wire after the P/R and do the KOEO test again. Make sure the return line is blocked completely or pressure will still drop. If it holds then you have found your problem. If it still doesn't create pressure check for leaks elsewhere. You said you replaced the injectors? Just making sure. I can't think of any easy ways to check this without equipment, but cycle the KOEO a couple dozen times. Then try to start it. You will probably be able to tell if a cylinder if full of fuel. ---Never done this just a thought that "might" work to check if an injector is stuck open. If that passes "which may not and still be stuck I have no idea-never done this, just a thought" then go back and pull the fuel filter. Crimp off the line after this spot and hook a pressure gauge here. It should hold. If not I would say it would HAVE to be either a lack of power going to pump or the pump itself. When you installed the pump you made sure to put it in the proper location inside the tank. If it's not in the designated area you may be just getting fumes. This is not the proper procedure for checking for fuel problems, but is an easy and accurate way to diagnose your problem. If none of this works or anything of what anyone else said, and it was mine I would just take it somewhere. YOu must have $500 + into diagnosing this problem. If this doesn't work you may have to swallow your pride. But I'm willing to bet if you post results of all these tests. "mostly the crimp after p/r and pressure test after filter with rest of line crimped tests" this will narrow down your problems to one of two things which will be very easy to trouble shoot. GL to you.
EDIT: don't crank on the pump when having the lines crimped. This procedure is looked to as a last result test and ins't good for the pump. Most dealers don't recommend doing this unless its necessary for dignostics. It won't kill a new pump doing it once or twice, but deserves a notation just F.Y.I.

Any results? get it figured out yet?

MyCARneedsHelp said:

Okay sorry i didnt reply but its been raining like hell out the past 2 days. Well im getting fuel psi with the KEY ON ENGINE OFF. It goes up to 33 psi when the KEY ON ENGINE ON and then ill drive it around the block and it will as soon as i get about 4 houses down the fuel psi cuts out and the car stals after i pump the gas i can hear it tryin to suck air in after a few pumps the car revives it self and runs. It only does this while the car is underload. I jacked up the tires in back and it ran just great. This is the 4 th pump, 3rd strainer,3rd sock, 3rd inersia switch and they are ALL FORD PRODUCTS!!!! wtf is going on. That cost me SOO much money im not even joking. I used my voltmeter and im getting power on everythin on Jrichker's list... im lost.

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You are losing electrical power, and at this point, it probably is in the wiring. Look closely at the fuel pump relay socket and wiring and the ignition switch wiring too. Hook up the voltmeter so you can monitor the fuel pump power at the connector closest to the pump and have someone watch it while you drive the car. A straight pin and some electrical tape may be needed to make this happen. Whatever you use, be sure to tape it up good so that it doesn't short out and fry the fuel pump fusable link.

You may want to try bypassing the relay and wiring directly from the battery to the fuel pump for test purposes only. Be sure to include a 15 amp fuse in the 14 gauge jumper wire from the battery to the pump. Check the pump ground wire while you are under the car.

One more vote for the map sensor and plus 5 agility to phatdaddy for mentioning it b4 me!

MyCARneedsHelp said:

I dont see the fuel pump ground

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The connector that joins the fuel pump wiring to the chassis has two wires, a pink wire and a black wire. The pink wire is power and the black wire is ground.

MyCARneedsHelp said:

as soon as i get about 4 houses down the fuel psi cuts out and the car stals after i pump the gas i can hear it tryin to suck air in after a few pumps the car revives it self and runs. .

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Are you saying you can actually hear the pump running constantly, even when these problems are occurring? I'm not sure I've ever heard a pump do this, but if you are saying you can actually hear the fuel pump sucking in air and fuel then I would have to say that the pump is installed correctly. There is a certain area in the tank that the pump must go. If you put it in a different way it will run off of fumes. Sorry if I misunderstood what you are trying to say.

Curious on update for personal knowledge.