if its an early 91 the fuel pump relay will be on the passenger side right behind the shock tower. late 91 it will be under the drivers seat.
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. If the fuse links 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 Relay: On 91 cars, it is located under the driver seat. 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. Theory of operation: Read this section through several times. If you understand the theory of operation, this will be much easier to troubleshoot. Refer to the diagram below frequently. Diagram of the fuel pump wiring for 91-93 cars. The electrical circuit for the fuel pump has two paths, a control path and a power path. 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. 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. Power path: 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: The location for the inertia switch is under the plastic for the driver's side taillight. There should be a round plastic pop out cover over it, remove it to access the switch button. With the test connection jumpered and ignition switch in The Run position as described above, 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. Pump wiring: Anytime the ignition switch is in the Run position and the test point is jumpered to ground, there should be at least 12 volts present on the black/pink wire. With power off, check the pump ground: you should see less than 1 ohm between the black wire and chassis ground. Make sure that the power is off the circuit before making any resistance checks. If the circuit is powered up, your resistance measurements will be inaccurate. Control path: 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. Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer and everything else is connected. Turn the ignition switch to the Run position and observe the fuel pressure. The pump should run at full pressure. If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad. If it does run at full pressure, the computer may have failed. Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn the key to the Run position. This can sometimes fool you into thinking the computer has died. Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin. With the ignition switch Off, jumper the computer into self test mode like you are going to dump the codes. Turn the ignition switch to the Run position. The light will flicker when the computer does the self test routine. A flickering light is a good computer. No flickering light is a bad computer. Remove the test jumper from the ECC test connector located under the hood. See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Engine Information Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the light blue/orange wire has shorted to ground. Remove the fuel pump relay from its socket. Then 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. If the wiring checks out good, then the computer is the likely culprit. Prior to replacing the computer, check the computer power ground. The computer has its own dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up next to the starter solenoid where the wire goes into the wiring harness
i got a new fuel pump relay and nothing, and i ran a jumper wire from the ECC fuel pump test point to a ground and still nothing. any ideas what it is? thanks for all the help
Betschart, run JRichker's list. You will find the issue. BK, your fingers got ahead of ya. The early cars had the relay under the seat. The late ones had the pump relay on the strut tower.
Ive read it a million times, it starts to confuse me, where exactly are the fuse links?I heard all the fuse links are by the starter cylonoid , but my car has a wire tuck from the previous owner.
Looks like you have a blown fuse link. Id check your fuse links by the starter relay. Make sure they have 12v on both sides of the link.
Alright thanks, Where exactly is the fuse link and how many is there, where is the starter relay? Thanks
Be sure you have either grounded the fuel-pump wire at the self-test connector or that you do your testing IMMEDIATELY after turning the key on (while the pump is priming out). If pink/blk has constant power but you don't have any other wires showing 12 volts, look for 12V at the red wire (at the relay). If it's missing, your pump won't power up (Read: the third power connector at the FP relay will not show 12V).
Posted via Mobile DeviceThe pink/black wire is the wire that goes directly to the pump.I'm assuming when the OP said pink wire, that he is meaning the Red wire from the ECM relay.That leaves the load side of the relay with no power.Reason why I mentioned the Fuse Link.
Joe, does this look off to you then?: http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif If I'm reading it correctly, it shows the pink/blk wire going to the common terminal. I thought this was weird (on my '88, IIRC pink/blk goes to the pump, as you noted). Either way, apologies for the confusion. And good call on the pink = red. I sometimes can't see traces and I thought that was what happened with him since he noted it was the only wire showing 12V, which made sense to me. I thought he was seeing what I thought to be the common-terminal input, based upon the diagram. Betschart, if your injectors and other components on the 'red' circuit have power, you might have an open in the wire before it reaches the FP relay.
The starter solenoid or starter relay is located on the driver's side inner fender near the battery. I think that the Mustangs with the fuel pump relay mounted under the driver's seat have a "mystery" connector. It is behind the driver's side kick panel that splices the pink/black wire between the fuse link and the fuel pump relay. I say "mystery" connector because I have never found it. Fusible link colors Link Gauge Color 20 Gauge Blue 18 Gauge Brown or Red 16 Gauge Black or Orange 14 Gauge Green 12 Gauge Gray
I was just going off the assumption that he had the wires mixed up. Thinking that the Red wire= all pink in his description. No confusion, as you are right. If the Pink/black shows 12v then it looks like the ECC relay is not sending 12v to the Fuel Pump relay. Or the Ignition Switch is not powering the ECC relay. As you stated, 12v at the injectors red wire is the tell tell sign.
where exactly is the ecc relay at? i heard it on the passenger side kick panel above the computer but i can not find.... thanks for all the help guys
