Alright I have an 89 5.0. It had stock seats. I bought some really nice corbeau VX2000 seats. I took out old seats and underneath both were wires. makes sense cause the original seats were electronic moving and stuff. I took out seat belts and clipped wires to clean it up. When I was done and tried to start car it would just crank. so I finally checked the fuel lines under hood and no fuel in them. I dropped gas tank and checked wires going to fuel pump, only 6 volts. I hooked up power wire from my amp (comes straight off battery for 12 volts) to fuel pump wire and the car started. So I consulted good old chilton and no info on fuel pump relay. checked all under hood and dash and couldn't find it. So I figured it was IN dash and I have taken apart the dash once and I don't want to do it agin so I found the fuel pump wire running along side the drivers side floor (right by door were all the other wires run along) I snipped it and bought some wiring and a relay from checker. Made my own relay coming off wire in floorboard plugged into AC fuse (Only has 12 volts when ignition is on) and then ran wire off fuse block and made another little spot for AC fuse. It works. Sometimes in morning I will crank it. Stop. Crank give it gas and it starts up. So anyway I just read in another forum that the fuel pump relay is under drivers seat. Is that true? If I did snip the relay off why did I still have 6 volts in the back of the car? any help would be greatly appreciated.
Help! My fuel pump
- Thread starter frmus3
- Start date
Yes, until 92, the fuel pump relay is under the drivers seat. I can't believe you didn't see the metal bracket and the relay under there. Not quite sure how you were getting 6 volts, but did you pull the whole wires out? You could just hook it back up to the wire from the ECU relay how it's supposed to be. Next time, you might wanna research before you go cutting wires out lol, wow.
Having to "give it gas" is actually cutting the injectors off on a fuel injected car, so you're probably running a little rich, and by cutting the injectors off, you allow the car to start.
Having to "give it gas" is actually cutting the injectors off on a fuel injected car, so you're probably running a little rich, and by cutting the injectors off, you allow the car to start.
i have no idea what you did wiring wise, but ill try to help. when you were playing under the seat, you might not have cut the FP relay harness, but could have shorted out the power feed wire. it is fed with a fusible link off the solenoid. that is the only way i can figure that you could have marginal voltage going back there (a partially burned link).
for some more schematic info see Tom's diagrams (look in the upper left quad of the page for FP info):
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
good luck.
for some more schematic info see Tom's diagrams (look in the upper left quad of the page for FP info):
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
good luck.
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. Use a voltmeter to measure the voltage drop across them. There should be less than .75 volt drop across a fuse link.
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 power for any actuator or relay, 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/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.
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. Use a voltmeter to measure the voltage drop across them. There should be less than .75 volt drop across a fuse link.
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 power for any actuator or relay, 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/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.
