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Thread: M-12071-a50 ford racing harness

  1. #11
    Club Member The Man's Avatar
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    Ac and Fuel pump relays are the same.....i was swapping them out when testing my fuel pump issues...
    Rick
    1993 Mustang LX Coupe

  2. #12
    Club Member JeffB's Avatar
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    I checked and both have the same part number.

  3. #13
    Club Member mustangmike6996's Avatar
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    So, if all else fails and it gest narrowed down to the relay, you can ship it to me and I can de-solder the AC and move it to the fuel pump location. There is another option, where you can solder a fuse holder pigtail to the circuit card and remotely locate the relays off of the board. The relays would be the standard automotive grade/size. The downfall is that it is not as clean of a build, but much more serviceable.


    So for the actual issues of the engine running poorly:

    The relay contacts could be sticking causing the pump to run intermittently. It could also be a PCM not commanding the pump to run.

    First thing that you need to check is the condition of all of the connectors.
    Crimps-solid crimping and soldering are key to good connections
    Water intrusion-Anything that may be exposed to rain or car wash water. Look for discoloration in the strands of the wiring.
    Grounds-high resistance. Sometimes this can be fixed but loosening and retightening the ground eyelets, but removing corrosion with a wire brush is best.
    Condition of wiring insulation. Anything routed close to the exhaust or bound up too tight/bent/pinched etc?
    Battery condition-fully charged and no corrosion on the terminals.
    Fuel pump motor-depending on age, the motor could be taking extra current to run or getting too hot and seizing.

    Measure supply voltage- you should be supplying very close to what the battery voltage is-to your ECM/relay module
    Measure ground resistance-you should see very few ohms of resistance. Check from the battery negative terminal to each ground eyelet. If one ground eye has high resistance, it could create a ground loop but attempting to ground through a different component (easier path)
    Voltage drops-basically, you are measuring how much voltage something is consuming.
    Your ground side should be less than 0.1VDC (measure from the negative battery terminal to the Ground supply)
    Battery positive should be less than 0.3VDC (measure from the positive battery terminal to the power supply IN)

    If that is all in good shape it will help lead you to isolating the fault and finding the root cause. Once again, the relay can be swapped but if something else is causing the relay(s) to overwork you will run into this issue again.

  4. #14
    Club Member JeffB's Avatar
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    I have done some checking with wires but will go through all of them starting at the battery. Would you be able to figure out if it is the fuel pump relay or the EEC relay? I like the idea of a remotely located relay. I would be very happy to ship this relay module to you. I will do all the checks you asked for then let you know what I find. Thank-You very much.

  5. #15
    Club Member mustangmike6996's Avatar
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    The remote relay thing could be a possibility. Depending on how much room you have where the module is located, I would suggest having all the relays use this style pigtail:

    https://www.delcity.net/store/Pre-Wi...SABEgKZx_D_BwE

    Then moving all the relays off of the board and easily replaceable in the future. Something like this:

    RelayMount.jpg

  6. #16
    Club Member JeffB's Avatar
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    I like that idea. I have room because I do not have a heater and have room behind the dash on the passenger side. I have the computer behind a kick panel on the passenger side. There is room above it and where the heater was. That way all the relays would not be obsolete.

  7. #17
    Club Member JeffB's Avatar
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    On the ground side I have .7VDC. There is a 9 pin connector that looks like there may be one bad connection. It has a little different color. The connector is the fuel pump wire. I will rework that connection. Let me know if you think the .7 is an issue. Thanks

  8. #18
    Club Member mustangmike6996's Avatar
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    0.7 VDC drop is pretty high for a connection. I would do what you said, clean and rework the suspect connection and keep going from there.

  9. #19
    Club Member JeffB's Avatar
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    I have went through the wiring and have the grounds down to .1 to .2. Reworked the main battery ground, that helped the most. I reworked the one wire connection also. I feel comfortable with the wiring now. The truck will start and idle. When I start to raise the RPM's the relays start to chatter and you can tell it is not running right. The fuel pump relay comes on now but does not shut off like it should.
    Last edited by JeffB; 05-25-2019 at 11:38 AM.

  10. #20
    Club Member mustangmike6996's Avatar
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    Quote Originally Posted by JeffB View Post
    I have went through the wiring and have the grounds down to .1 to .2. Reworked the main battery ground, that helped the most. I reworked the one wire connection also. I feel comfortable with the wiring now. The truck will start and idle. When I start to raise the RPM's the relays start to chatter and you can tell it is not running right. The fuel pump relay comes on now but does not shut off like it should.
    It sounds like a failing relay, weak coil or sticking contacts. I'll PM you my address if you still want to ship it up for me to repair.

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