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BobCat 743B fuel shut-off problem, no start

Discussion in 'Skid Steers' started by bkeese, Aug 12, 2019.

  1. bkeese

    bkeese Member

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    OK my 743B will not start, just cranks fast (new battery). I just replaced the oil pressure switch. The old one had a lug broken off but it still ran with out it. I replaced the switch while my son rebuilt the drive motor. After reassembling it wouldn't start, just cranks. I can hear the solenoid click most times when the switch is turned on. I replaced the key switch, it was bad, but didn't fix the no start. My son noticed the fuel shut-off was clicking to ON when the key is moved to RUN, but is would click off when trying to start. I have owned this machine for many years, but I noticed a loose zip tie on the Fuel shut-off linkage so we tried the slip it over the lip on the HP casing and it started right up, except now it won't stop.

    It fairly clear that there is a sensor telling it to Not To Start when cranking and the Fuel Shut-Off does not turn on when the key returns to On after start. In an Auto this is a classic ignition switch issue, but I don't believe it is here. Same problem with 2 different switches. Any idea which sensor is messing me up?
     
  2. thepumpguysc

    thepumpguysc Senior Member

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    Is your sol. the 3 wire w/ the big rubber boot.??
     
  3. thepumpguysc

    thepumpguysc Senior Member

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    Black is - ground
    White is PULL-IN.. hi amp from starter.
    Red is HOLD..
    IF the sol. isn't adjusted correctly it wont pull in.. or hold.
    TRY to manually pull it in w/ alittle pressure from your hand when cranking & see if that helps.
     
    kshansen likes this.
  4. bkeese

    bkeese Member

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    Thepumpguysc: If I pull it while cranking it starts and yes it is the 3 wire solenoid. I unconnected it and noticed some corrosion on 1 terminal. I'm going to clean it up with a small file and see if that works.

    Thanks
     
  5. thepumpguysc

    thepumpguysc Senior Member

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    The PULL-IN should come off the starter.. IDK where the relays are to switch over to "Hold"..
    & it IS possible that the pull in coil inside the sol. is bad..
    Does it JUMP UP out of your hand when u "help it" up.. or do u have to get it all the way up & then it holds.??
     
    kshansen likes this.
  6. bkeese

    bkeese Member

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    It does not jump out of my hand or stay when pulled all the way back. In fact when it starts by holding the solenoid back and letting go it stops. With the key ON I've got 12.12 volts on the RED and 5.75 on the WHITE wire. When to key is turned to start (engines cranks) the Fuel Shut-off goes to OFF, the RED wire voltage drops to 8.5 and climbs to a little over 9, the WHITE wire drops to 4 volts.

    What is the IDK? Is there a relay involved here? Could that be an issue? Where is this relay? Does the voltage drop indicate possible corrosion at the starter?
     
  7. Vetech63

    Vetech63 Senior Member

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    Is there a capacitor in the wiring loom of your solenoid? It would be between where the wiring goes into your solenoid and the solenoid plug in.
    I am assuming you have the standard colors of red, black, and white on your solenoid.
    Black = ground.
    Red = hot with the ignition on and usually has a fuse in the system. (hold coil)
    White = hot when the starter motor is engaged only. (pull coil)

    I have seen a lot of different variations of the wiring colors and even some that look exactly like the standard coil but operate and are wired differently(capacitor solenoids especially).
    Take a picture of the entire solenoid and wiring if you have any doubts and post it here.
     
    mg2361 likes this.
  8. bkeese

    bkeese Member

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    No capacitor just bare (Black, White and Red) visible wires.

    Now the fuel shut-off is clicking twice (on then off) in a second or 2. I also noticed that there is a square box mounted on the side of the machine, it also clicks twice. I think the parts manual calls this a timer/25a fuse (6669415/6670808). Can this be the cause of my problems? What does this Timer do?
     
  9. thepumpguysc

    thepumpguysc Senior Member

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    The timer drops off the voltage if the engine hasn't started in x amount of time.. to keep the sol. from burning up.. seeing its drawing a lot of amps from the starter circuit.. I think..
     
  10. bkeese

    bkeese Member

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    Well, I need to pull the trigger. It seems that it only takes 5 volts to hold the fuel shut-off solenoid and I have that and it won't hold it, I thinks the solenoid is bad, but the timer could also be bad. Pay your money and pick one.
     
  11. Vetech63

    Vetech63 Senior Member

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    Just use a charged 12 V battery to check your solenoid. Ground the black wire and just touch the white wire to the + post. It should do a quick pull in when you touch the white wire...…….if it does then the pull coil is working. Then put the red wire on and leave it there...………..push in shaft into the coil to bottom it out...……..it should stay there magnetically until you remove the red wire. If you leave the ground and red wires hooked up, you can strike the white wire on the +post and it should pull in and hold there on its own.
     
    mg2361 and thepumpguysc like this.
  12. thepumpguysc

    thepumpguysc Senior Member

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    That's how we did it at the shop..^^^
    But that "Pull-IN" takes A LOT of amps to work..{white} U may have to "help it" a little..
    Our tester had an adjustable AMP knob..