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Thread: Fuel pump not priming but works on it's own

  1. #11
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    Yeah, measured at the leads that connect directly to the pump motor (pump unplugged). Pump harness is connected to the bike harness. The 6V comes on with the flip of the engine kill switch, so the current behavior seems correct (just incorrect voltage output). I'll remeasure the voltage at the bike harness connector with the fuel pump disconnected, isolating the pump system from the rest of the bike. I'll also see if I can't measure a resistance through the wires in the fuel pump system itself, but it seems like the issue is on the bike harness side, just no idea where. Is there a way to jump the wires at the ECM connector to create a running condition? i.e. jumping pins 1 (gray) and 3 (brown w/yellow)?

    I'll also, for good measure, go through and clean up all of the ground connections on the bike to see if that's causing a problem somehow.
    This is all really throwing me for a loop and not expected when just changing out a battery. Does the regulator or anything need to be submerged in fuel for any reason?

  2. #12
    Senior Member Cooter's Avatar
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    No need for testing for resistance of the fuel pump, you have 6V at the plug when its disconnected.
    6V at the pump is not enough, and big clue
    Nothing needs to be submerged to test
    I am assuming you really did swap relays already, I am assuming it does crank ok.

    My testing laid out above will find the problem if you follow the steps.

  3. #13
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    Well it seems like doing continuity checks isn't enough, and I need to move on to doing resistance/voltage tests. 6V isn't enough to run the pump, but it shows that continuity exists between both 30 and (+) at the battery, and 87 and the power at the pump. There's added resistance somewhere, I just have to figure out where.
    I'll need to pick up some contact cleaner and thoroughly clean the connectors between the pump and bike harness. I'll also clean the connections at the relay and its socket.
    The ECM plug has never been removed prior to this issue, and the plug itself looks clean but it wouldn't hurt.
    And as mentioned before, I'll likely clean up all of the ground connections.

    Would it be worth my while to pick up a test light?

  4. #14
    Member TapRoot's Avatar
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    If you know that the brown/yellow is the ground for the pump and the gray signal wire provides 12v then check the gray from the pump to a good ground you should get 12v if so you are getting signal. If you only get 6 v to the brown and yellow then most likely the ground wire is the culprit. You should be able to put your digital MM on the diode scale and get a dead short from a good ground to that brown/yellow, if not I would think itís the culprit. Now if you jump out the brown/ yellow to gray at the connector and you have a dead short reading at the pump this would tell you the wire is at least not broken and your problem is within the connector, ecm, ecm ground or shorted to another wire. This is my logical thinking looking at the schematic and being an electrician, not to say Iím right so I guess take it with a grain of salt, Iíve only owned a Buell for 2 seasons.

  5. #15
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    Okay, I'm getting 12.8V between the gray wire at the pump and a good ground. Checked a couple grounds just to be certain and they are consistent.
    So that isolates the brown with yellow wire, however, I'm not fully understanding your explanation about setting my multimeter to the diode scale and getting a dead short between ground and brown w/ yellow. Isn't the diode setting directional? Or should I be getting a short (0L) regardless of probe direction?
    I'm a mechanical engineer, and I've dealt with a fair amount of light electrical work, but I'm not nearly as familiar with diodes

  6. #16
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    Out of curiosity, I disconnected the ecm and jumped the black and brown w/ yellow wires on the black plug. This caused the fuel pump to run.
    Not sure if this provides more info or not

  7. #17
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    Honestly, it's as if the ECM doesn't want to connected the brownw /yellow wire to ground.

  8. #18
    Senior Member Cooter's Avatar
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    "Well it seems like doing continuity checks isn't enough, and I need to move on to doing resistance/voltage tests."

    Same thing man. "Continuity" in this case means there is acceptable resistance in that circuit, allowing full voltage through it.


    The ECM does not power the fuel pump, it activates the relay ONLY and relays are only ON or OFF. No "6V" BS. It connects the 30/87 circuit to power the pump.

    So, do you have 6v at the pump plug when activated? And 12.8V when testing with a good ground (ground path is compromised)

    OR

    does it run when you manually trigger the relay from the ECM plug? (ECM is toast), did you hook up the battery backwards when replacing it?

    Bad clues, so confuse.
    Last edited by Cooter; 08-23-2019 at 07:41 AM.

  9. #19
    Member TapRoot's Avatar
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    Yes the diode scale is directional but if the connector at the ecm is off and the pump connector is disconnected then this should isolate the wires and if you had b/y and gray jumped at the connector or pump then you should read a dead short with polarity either way and OL between the two when the jumper is pulled. If you are picking up significant resistance with the wires open then I would say either of the two may be shorted, also it gives a nice audible when checking for ground faults as you probably know but if you prefer the Ohms scale that’ll work also. If all worked before and all you did was change a battery there is a chance something may have gotten shorted or taken a spike. Maybe Cooter or someone else may know but does the b/y rely on the pumps ground within the tank for completing the circuit? If so, this could bring your pump back into play but I’m not sure. I guess if you were able to manually jump it out at the connector to get it to work then the ground should be good. Not sure if this is even a good idea but if you jumped the b/y to a good ground then all should work I would think? Would this narrow it down to the ecm and would it need to be jumped before the relay to Eliminate one of those possibilities? Just trying to spit ball here

  10. #20
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    Cooter,
    Yes, technically continuity check and voltage/resistance checks are the same thing. On my meter, I have a separate continuity check setting that simply beeps when there is a good connection. This is separate from the settings from where I measure voltage or current. So for me, a continuity check just provides a little less detailed information as opposed to voltage/resistance, but there wasn't a way for you to know about my specific meter. My fault there.

    I understand that the ECM does not provide power and it's basically a solid state relay (from what I can tell). The 6V thing is strange (I think it was reading a steady 4.5V yesterday when measuring between the gray and bn/y wires), and I'm tempted to discount that as user error.
    Yes, when I remove the black plug at the ecm and jump the bn/y wire to ground (black wire) the pump runs. Honestly, that more or less seems to isolate the ECM, unless I'm missing something else.

    As for cause, battery was not installed backwards. The original battery was attempted to be jump started via push starting the bike, which worked, albeit for only 200ft or so. There was a voltage error with the fuel pump error originally, but I chalked that up to the original battery being dead. It's possible that it could have been a high voltage spike that damaged the ECM.
    At this point, I think I'm going to grab a used ECM from ebay. $160 isn't the end of the world, just annoying.



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