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  • Bobcat issue

    I originally posted this on the Hobart board. I've been waiting for some time to get posting permission here so here it is:

    I have a Bobcat 250NT circa~2005 with a problem I'd like some help with. It started out with the classic "won't idle down" issue. Most common causes would be: 1. Faulty idle solenoid, 2. Faulty idle control module. Here's the diagnostic procedure performed:

    1. Test solenoid
    1.1 Check resistance at terminals. - Result: 26 ohms
    1.2 Jump power direct from battery. - Result: Solenoid energizes, but it's not strong enough to overcome the throttle spring.

    2. Test Idle control module
    2.1 With welder running in run/idle mode test for voltage at solenoid leads. - Result: Solid 13 volts present when machine should be idling.

    Given the above results, it would seem obvious that the solenoid is faulty, so I replaced the solenoid and now the problem is different. Now, while in run/idle, the machine tries to idle down for just a split second roughly every two seconds then continues running at full speed. Voltage measured at the solenoid spikes to 13v every two seconds then immediately returns to zero. It's as if the load from the solenoid is overloading/tripping the idle control module and it's getting caught in a trip/reset loop. For the record, the new solenoid measures 11.5 ohms, and when jumped directly to the battery it is strong enough to pull the idle down. All this would seem to indicate a faulty idle control module.

    While in my experience it's uncommon for two components to fail simultaneously, it's not unheard of. So am I missing something here? The only two theories I have are 1. Both components failed and I also need a new Idle control module. 2. Only the solenoid failed and the replacement I got is drawing too much current and tripping the idle control module, though this seems unlikely because 11.5 ohms at 13 volts would only draw 1.13 amps, and I would think the module would be fine with that.

    I would appreciate any input before I drop $150 on a module. It would also be useful to me to know the resistance of a working idle solenoid if anyone has one they could measure for me.



    Update:
    I had a chance today to spend more time on this. First, I opened the idle module. The cover can be easily removed, but as I suspected the board is potted in the case, so it's not serviceable. Second, I installed a relay between the idle module and idle solenoid so that the relay can take the load as opposed to the module and now the machine runs as it should. I did this as an experiment, but now that it's working I'll probably run it like it is until I can get more information on this (like what the resistance of the solenoid coil should be).

  • #2
    Welcome!

    You have probably identified the cheapest possible solution to your problem! I don't have direct experience with that idle module, but I think there are others here who will probably be able to help.

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    • #3
      It sounds like there is nothing wrong with either. You don't have your sol. plunger going to the bottom like it should

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      • #4
        Originally posted by Popscott View Post
        It sounds like there is nothing wrong with either. You don't have your sol. plunger going to the bottom like it should
        I actually thought of that already. I made sure the solenoid almost bottoms out, probably about .050" short of bottom to be sure the carburetor is pulled tight against the idle screw.

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        • #5
          It's the ground wire going to the base of the machine from the engine.
          The module either works or it doesn't.
          Last edited by 1997CST; 02-28-2020, 07:32 AM.

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          • #6
            Back the idle screw out of the way.... Adjust with the sol only.(yea the muffler gets hot)... as close, if not a little slower RPM...only use the screw to fine tune it back to final idle RPM.
            Last edited by Popscott; 02-29-2020, 09:46 AM.

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