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  1. #1
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    Default 86 Capri efi fuel circuit help

    I am trying to start 86 capri with efi. The car has not been started in years probably 15. it was a tow yard recovery with no tank or pump. I bought a new tank and pump. Now i have no voltage to the pump. The relay under the seat has voltage and the inertia switch has voltage but none at the pump. Can anyone explain the circuit? I am going to buy an evtm manual but need to move the car asap. It will hit and run with a little carb cleaner squirted in the intake. But i need to know how the circuit maps out. Thanks

  2. #2
    FEP Super Member xctasy's Avatar
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    Haystack here is a former Ford service technician, and the standard "out in the field" method is to try this.

    Quote Originally Posted by Haystack View Post
    https://youtu.be/z0ehA8cFTkc

    here's a quick video I did of pulling codes with a paperclip and you can use a voltmeter or a test light
    then he looks via fault to the system in question. This was a fuel injector matter, so.....

    Quote Originally Posted by Haystack View Post
    Now, go to Google, type in "sbftech efi no start". 10-20 minutes later, you will pretty much know exactly what's wrong and not waste anymore time or money.

    You do not need a "noid light". A volt meter or a test light will do. I actually use an extra tail light but that I soldered a wire onto.

    All you do is verify that you have power at the injector, then look for a flashing light. If the light doesn't flash or flashes intermittently, it could be the pip or tfi module, but it could also be a bad ground or a plug you might have forgotten to plug in.

    One reason I say to pull codes, I had a car randomly die on me. Turns out the new tps sensor I swapped in wasn't all the way in the connector. Pulling codes told me bad tps so I looked over and saw it was sitting funny.
    Sensor or computer or relay problems are pointed to by the fault codes. Use them!

    Spout problems happen and its all potentially hard to trace. People fiddle with MAP sensor, MAP sensors go bad, people change computers, and don't understand the loop wire to O2 and/or Neutral safety switch, so if someone has been into the computer, doing these basic checks are your first que to call.

    Care of Jeff at https://www.stangnet.com/mustang-for...-30-46.832635/

    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
    ground.

    Diagnostic connector close up



    Underhoodpictures007-01.jpg




    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 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). Notice that
    pin 19 on the computer is the monitor to make sure the pump has power.
    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.


    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.

    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.



    The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds.
    One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump
    may be larger gauge wire that the fuel tank sender ground wire.

    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.

    You should see less than 1 Ohm between the black wire(s) and ground. To get some idea of what
    a good reading is, short the two meter leads together and observe the reading. It should only be
    slightly higher when you measure the black wire to ground resistance.

    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.

    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.

    Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green 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 Tan/Lt Green 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

    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.

    See the following website for some help from Tmoss (diagram designer) &
    Stang&2Birds (website host)

    http://www.veryuseful.com/mustang/te...itchWiring.gif

    http://www.veryuseful.com/mustang/te...nks-ign-ac.gif

    http://www.veryuseful.com/mustang/te...1eecPinout.gif

  3. #3

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    I assume this is for a 5.0 v8 entine? If so Power is sent down a red wire from eec relay to intertia switch. From there it runs to the coil side of the fuel pump relay on a red and black wire. the coil is grounded at the pcm through a teal and light green wire. The switch side of relay should have 12 constant at the yellow wire. This is fed by a fuse link on starter solenoid. The relay switches power to the pink and black wire. Runs to pump and grounds on the black wire. The ground also shows to have a .68 ohm resistance wire. Hope this helps
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  4. #4

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    I just have to correct a statement here, I am in no way a former service tech. I have gotten pretty good at troubleshooting, having driven $500 fords for the last 15 years though.

    Everything else said I believe to be true though.

    On one if my cars, I fought a random fuel pump failure for months. It ended up being both the inertia switch failed (put out less then half voltage) as well as a bad splice by the previous owner to the pump itself. Verify good voltage from the relay, then check for voltage drop at the tank. Not sure where the mustang inertia switch is, on my car its right by the trunk latch or near the passenger side hinge along with the relay.

    The power is fed from a fuseable link to the ignition switch, then to the computer relay, and then finally to the fuel pump relay and lastly to the inertia switch. Any failure along the way will cut power.

    You can also jump the fuel pump relay with either a paper clip or a test light, just to rule out a connection problem.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  5. #5

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    Good call on power from fuse link off the ignition switch, l think your right on that. The diagram in alldata is showing the intera switch after eec relay and before the fuel pump relay. However they aren’t always correct either. ​
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  6. #6
    FEP Super Member xctasy's Avatar
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    https://www.stangnet.com/mustang-for...xperts.882848/

    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.

    The location of the inertia switch wiring in relation to the fuel pump depends on the model year of your Mustang. There is the troubleshooter for 87-90 model Mustangs
    http://forums.corral.net/forums/gene...ia-switch.html

    Convertible, behind the interior panel, back driver's side (basicly on the other side of the tail light)

  7. #7

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    Its been a year or so since I messed with my car, but to me it would make sense to put the inertia switch after they relay. My thinking is that it would be double redundancy after the relay, but it wouldn't be before.
    2 1986 cougars (both 4 eyed and 5.0)
    1 1987 cougar

  8. #8

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    I think it makes sense to have it before. In the event of a crash it will cut 12v from reaching coil side of the relay. This way if the control wire is shorted to ground due to the damage it will not continuously run the pump
    84 LX Vert. 5.0 5speed canyon red on white
    99 cobra, electric green on medium parchment, vortech s-trim

  9. #9

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    The fuel pump relay requires two 12 volt sources.

    1. Key On power
    2. Steady always on power

    The key on power is fed from the ignition switch. When that plastic switch under the column plastics fail, it separates, and you lose key-on power to the relay.

    The 12 volt constant is fed from the fuseable link and goes into the relay. When you turn the key on, it sends 12 volt power to the relay under the seat. From there, it turns the relay on, which then Diverts power to the constant on wire, hence running the circuit off of the always on line.

    with the key in the on position, verify you have both sources of 12 volt going into the relay. If you only have one source, turn the key off. Probe the relay. If you know have nothing, then the constant 12v power is missing. Troubleshoot that circuit. If you do have power with the key off, then your key on power isn't working and you should look at that white ignition switch below the key.

    If you have both sources of power, then you need to leave the key on, and probe for a single power source going into the cutoff in the trunk, and make sure power is going into the cutoff, and coming back out to the fuel pump

    Check the link in my sig for the full 86 electrical and vacuum ford diagrams
    Jeremy
    -86 mustang SSP X CHP Unit # 3788-bone stock & staying that way
    -66 Mustang, bench seat car,8.8,t5 fuel injected 92 engine
    -72 Maverick 5.0 resto in process
    -12SS Camaro 6 speed. 600 FWHP, Kraftwerks Supercharger
    -03 z71 Avalanche 9" lift on 35s Daily Driven 20k a year. 290k miles at 11.8 mpg
    Entire 1986 electrical and vacuum troubleshooting manual download
    http://slantnosefox.com/picturehosti...g%20manual.zip

  10. #10

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    If you have near battery voltage on one side of the inertia switch but no voltage at the pump, then I would say that the problem is most likely the inertia switch and then a wiring issue. My 88 Tbird had a bad inertia switch that I had trouble diagnosing, mainly because I was using a test light. I finally tested the voltage into and out of the switch. I discovered 12v was going in, but less than 10 was going out to the pump. I unplugged the connector from the switch and it was melted. This was a standard problem with the 1st type of inertia switches. You can unplug the inertia switch connector and jump it with a paper clip. Do this as a test only! If the car runs, you've found the problem.

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