new parts no start...

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by jcgafford, Feb 4, 2012.

  1. installed the new fuel tank and fuel pump. now the pump runs constantly. at first i searched for reasons that it could do this, such as the regulator failure. after further snooping around there is a hiss under the upper intake that sounds like air, key on engine off, no fuel to be seen around that area. there is a "bleeder" on the fuel rail that i checked and there is fuel to the rail. pulled front drivers side spark plug and it was dry. so fuel to the rail but not thru the injectors??? plan on pulling the top of the engine soon and pulling the rail, any other suggestions?
  2. can you smell fuel? if its pumping it out then you should smell fuel. When i did my first pump i wired the damn thing backwards and it ran constant. Figured it out quick and cussed myself the rest of the day.
  3. well.... i assumed i had hooked the fuel lines up backwards, took the tank down and "checked". after my fuel bath it occurred to me that i had already realized they only go on one way. so smell fuel? sure all the time ha! but as for wiring it was the same way as the lines, only one wire could go to each terminal on the pump as they were different sizes. it does have a "leak" of some sort up front, i can hear it. but no visible fuel. i assume the "leak" i hear is causing the fuel pump to run, but then again fuel should be all over the place... i am at work right now and trying to trouble shoot it from 10 miles away. probably pull the upper intake tonight and have a look.
  4. Are you saying with key on, engine off that the pump runs full time? I believe (and I could be wrong) that the computer runs the pump for its initial 3-5 seconds for start prime. Could be a stuck fuel pump relay. I'd also check codes.
  5. yes, key on engine off it runs. there is a hiss under the intake near the fuel rails that i could not get torn down to to look at. but no visable fuel. the bleed for the passenger rail has fuel, so i will tear the rails off and clean the fuel injectors while i am there. try to find that leak. no scope for codes so that will be the next purchase.
  6. well it was the fuel pump solenoid? the little switch that shuts it off mounted on the passenger fender well. pulled cleaned and that was that.
  7. Doesnt make sense to pull the top of the motor for a constantly running fuel pump? If your fuel pump wont turn off its purely electrical not mechanical. My FIRST check would be the relay. Second would be check the relay.... If a relay has gone bad cleaning it wont fix it...

    edit: Just realized your post said you fixed it, was there corrosion on the contacts of the plug or relay? For the 15 bucks it costs I would just recommend replacing the relay before it leaves you stranded.
  8. Just for future reference. That hiss you were hearing was not a fuel leak. It was your fuel regulator doing it job and returning unused fuel to the tank.

    Sent from my HTC Aria
    jcgafford likes this.
  9. You dont need a scope to read codes. There's about a billion posts in here on how to do it without the reader. Although I bought my reader from Pep Boys for about $30.
  10. no corrosion, water.... frozen. and yea gonna buy the new ones.
  11. thats my plan, hate test lights.
  12. See the next to last paragragh for a possibe solution to your problem...

    Fuel Pump Troubleshooting for 91-93 Mustangs

    Revised 21-Oct-2011 to Add location of fuel pump relay on 91 model year cars
    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 upper RH corner to

    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 upper LH corner to



    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's seat.
    On 92 and 93 cars it is located under the MAF. Be careful not to confuse it with the A/C WOT cutoff relay which is in the same area. See the diagram to help identify the fuel pump relay wiring colors.
    Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
    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

    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
  13. thats what got me to check it, looked at your thread right away then searched for the location. there is another relay right next to it. any idea what it controls?
  14. On the 92-93 5.0 Mustangs, the relay in closest proximity to the fuel pump relay is the A/C WOT relay. It turns off the A/C compressor when you hit Wide Open Throttle. At that point the A/C compressor draws no power from the engine and acts as an idler pulley to provide belt routing.
  15. gotcha. i originally switched the relays and it worked. then cleaned everything up and switched them back and it still works. going to replace both just to be sure about them. thanks