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  1. #1

    Question HELP! MSX 140 fuel problems!

    I have a msx 140 after cranking for about 20 sec. it will start. If I hold the throttle down it will take off for a few seconds then die back to about 10 mph. If you continue to hold the throttle wide open it eventually will take off again for a short period of time. I do not hear the fuel pump kick on when I bump the start button nor do I have any fuel pressure. However when I bump the start button and check the connector on the fuel pump with a volt meter it reads out at about 10.6-11.1 for about 15 seconds then goes back to 0.00 after. I can also hear some fuel slosh in the tank when I bump the start button.

    I am thinking I have a bad fuel pump but not sure, any help would be much appreciated.


  2. #2
    I do not know where the fuse for the fuel pump is located but I assume it is good if I am getting power to the volt meter.

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by koryk View Post
    I do not know where the fuse for the fuel pump is located but I assume it is good if I am getting power to the volt meter.
    On the MSX 140 the fuse for the fuel pump is hiding inside one of the wire splice connectors, near/above the battery. There are two fuses in there.

    The way the MSX 140 fuel pump works is that the fuel pump ALWAYS has full battery power (via the fuse) to one pin of the connector. The opposite pin on the fuel pump connector has a Brown wire which goes directly to the EMM (pin-40). When the EMM wants the fuel pump to run, the EMM grounds the Brown wire. This causes the fuel pump to run. All Ficht engines are the same in this regard.

    There are two other connections at the fuel pump connector, those are for the fuel level sender signal to the display.

    Your voltage measurements seem odd. Full battery voltage at the fuel pump should be higher than 11.1 volts, and should be constant, all the time.

    The fuel pump is NOT connected to the Start button. The start button simply cranks the engine. That's all.

    The EMM watches for signals from the magneto and the Crank Position Sensor to determine that the engine is rotating. Then the EMM 'wakes up' and grounds the Brown wire to get the fuel pump running. Shortly afterwards it starts supplying spark and injecting fuel.

  4. #4
    Maybe I need a little schooling on how to diag.

    The red/white wire is reading 12.61v
    The brown wire is reading 0.00

    Thanks for the reply!

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by koryk View Post
    ... The red/white wire is reading 12.61v
    The brown wire is reading 0.00

    Thanks for the reply!
    Did you disconnect the connector to take these readings? If yes, then not useful.
    Tricky situation, but the Brown wire measurement is only useful when actually connected to the fuel pump connector. The voltage for the Brown wire comes through the fuel pump, from the 12 volt feed on the same connector.

    If this was with the fuel pump plugged in but NOT running, engine NOT cranking? Then the fuel pump core has failed, or the internal pump wiring has failed.

  6. #6
    That was unhooked. I gave it a shot hooked up but am at a loss. How do you get a reading with it connected? I don't really want to skin the wires.

  7. #7
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    Quote Originally Posted by koryk View Post
    That was unhooked. I gave it a shot hooked up but am at a loss. How do you get a reading with it connected? I don't really want to skin the wires.
    I sometimes use skinny pins I steal from the sewing kit

    Slide the pin down alongside the wire, into the back of the connector. Try not to slice up the water seals. Wiggle around to find a solid contact.

    If I get frustrated I sometimes just pierce the Brown wire with the thinnest pin I can find, on an angle. Then I don't tell anybody

  8. #8
    10-fo thats a good idea. Ill give it a shot in the mornin, the whiskeys set in and im tired of messing with it tonight! Thanks a ton for all the help.

    If ya got a sec could you check out my other post.
    http://www.greenhulk.net/forums/showthread.php?t=195997

  9. #9
    Ok red/white and brown wire read about 12.59 when plugged in. I'm assuming that means my pump is good? What do I check next?

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by koryk View Post
    Ok red/white and brown wire read about 12.59 when plugged in. I'm assuming that means my pump is good? What do I check next?
    Ground the Brown wire, using the pin connection. The Ficht fuel pump should run at full normal flow, and deliver pressure against the pressure regulator (which is inside the fuel pump body, at the fuel return fitting).

    The normal fuel pressure at the Schrader valve tee when the electric fuel pump is running is something over 20 PSI, typically about 23 PSI.

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