Need Help!! Miller 250 NT crank NO start
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  1. #1
    Join Date
    Jul 2010
    Location
    NE North Carolina
    Posts
    3

    Question Need Help!! Miller 250 NT crank NO start

    Need help guys this one has been running me around for over a week. A 2003 model miller 250 NT with Onan 20.5 hp engine. Engine will crank but no start. (1) new fuel pump OK. No current to anything except grey wire (oil pressure switch) in run idle. Here is what I have done so far. NO "snap or click" when switch is turned on.
    Fuel shut off works with external 12v. No voltage otherwise.
    Stop diode measure of continuity OK to values
    Fuse in Harness OK Diode checked with digital meter .779 / analog @1k .4 @10k .8 values in one direction only (seems to be OK)
    Stop relay test OK
    Here is where I get in real trouble. 12v at engine to welder plug (red) 12v at switch.
    Switch on run idle 12v to grey (oil pressure switch) Run 12v to grey.
    Switch start 12v to yellow (start)
    Switch to run Idle 12v to grey oil switch wire and to H term on PC module (pull to Idle) NO current out of Module not even to hour meter.
    Switch to RUN Grey only (oil pressure switch)
    I am left scratching my head, to beleive that I have a module problem, should I not have another 12v leaving the module to the blue wire (reason for diode in yellow line to prevent startup) blue wire +red +white at pressure switch has nothing. Or am I not interpting the oil pressure switch correctly. Is there a test for the module somewhere please send a link for guided step by step test. PLEASE HELP Thanks

  2. #2
    Join Date
    May 2008
    Location
    Orange, TX
    Posts
    11,271

    Re: Need Help!! Miller 250 NT crank NO start

    Got a SN?

    You've certainly done a pretty thorough troubleshooting job but the module you refer to is the engine idler control and related to the ignition only in that it gets powered up at the same time.

    The diode (D8) is the oil pressure by-pass for starting. It allows (+) battery voltage to feed the RUN circuit beyond the OP switch (fuel shut-off solenoid, stop relay CR1, electric fuel pump and Idler control board) during cranking for starting prior to the engine building oil pressure sufficient to close the oil pressure switch.

    You didn't indicate if you checked for voltage at any of the RUN circuit components listed above in the START position which would confirm if the oil pressure by-pass circuit is working properly. Until there is oil pressure sufficient to close the oil pressure switch, there's no other way for battery voltage to get to the RUN circuit beyond the OP switch.

    Check the oil pressure by-pass and OP switch by checking for (+) voltage at the output terminal of the OP switch while cranking. If diode D8 is good as your test indicated you should get a voltage reading immediately in the START position. If D8 or the circuit is bad and the OPswitch is good, you should get voltage at the switch output within a couple seconds of cranking. If no voltage at all after several seconds of cranking then I suspect you have a dual fault - bad D8 or by-pass circuit and defective OP switch.

    The components I would suspect are:
    1) Stop relay CR1
    2) Fuel shut-off solenoid
    3) Ignition coil
    4) Electric fuel pump - if so equipped

    Have you checked for spark at the plugs while cranking? If no spark, remove the wire from either terminal #30 or 87A on the stop relay and try again. If still no spark the ignition coil is suspect.

    If you have spark while cranking then the stop relay and ignition coil are OK and I would suspect the fuel shut-off solenoid or electric fuel pump if so equipped.


    Let us know and if I think of anything else I'll post it up.
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  3. #3
    Join Date
    Jul 2010
    Location
    NE North Carolina
    Posts
    3

    Re: Need Help!! Miller 250 NT crank NO start

    duaneb55,

    Thanks for info, here is the rest of the story. Miller SN Lc550315 Onan mod P220 GIOHV-2252A 2003 w/274 hrs. like new, (doesn't matter if it is garage kept and looks brand new if it won't run. Just as a reminder I do not get the electrical "snap" of relays and or solenoids when I turn switch to run/idle from stop anymore.

    No elec fuel pump, Robin Subaru vac opperated. Vac and oil level good. Fuel pressure good.

    I may not have been clear on the fuel shut off solenoid, in the orginal post, fuel solenoid works with outside 12v i.e. bat. Does not work nor is there 12v at the connection behind the engine cover *Except during start* No current at run/idle run, which should have current 12v at this time.

    Coil(s) OK hot spark. 12v on grey wire OP (input)? at run run/idle

    I have voltage output at op almost immediatly, of cranking of 10.5 to 11.0 v A little low but a lot of testing and some draw to starter.

    Stop relay spades 30-87a closed (continuity) 12v on 85-86 30 -87a open no continuity (seems to be OK?) 12v to cr1 only during start.

    The run circut seems to be in question I cannot read blueprints well enough to know what to do. What little bit I know usually gets me in trouble. There does not seem to be 12v coming back to the welder/engine plug from the switch side other than the grey oil pump input wire, or if there is suppose to be. My question is if the diode (D8) is to stop 12v from backing up to the start circut on run run / idle (with swictch just turned on) then where does the 12v come from? Or is the input side or grey wire of op the only 12v source. If that is the case where did the "snap" of relays and or solenoids in run/idle run get to?

    I can cross red to blue (at engine plug) w/plug unplugged and I get my solenoids and relay *snap* maybe I should not have done this, but it wasn't running anyhow.

    I can (spritz) fuel in carb and welder will start and run for a few seceonds. If I could get this run circut to work I think it would be fine

    Your first post said to totally forget the pull to run module and so I have.
    Somewhere in front of me (something simple) there is no 12v getting to the run side.

    Hope this information is not confusing, if so we'll come at this at a different angle. Now I'm confused

    Thanks Again and waiting to here back from you.

  4. #4
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    2,464

    Re: Need Help!! Miller 250 NT crank NO start

    If it starts and run for a few seconds with a spritz of gas or carb cleaner. Then you have a fuel problem. If this unit has set for a while, you may have to open the carb. and free up the the gas valve in the bottom of the fuel bowl. some people call is the anti-backfire valve.
    The valve may sound like its working but part of it is not working.
    Hopefully this is not a sealed C.A.R.B. carb we have on the new units here in california.

  5. #5
    Join Date
    May 2008
    Location
    Orange, TX
    Posts
    11,271

    Re: Need Help!! Miller 250 NT crank NO start

    I agree with ccawgc - fuel delivery problem.

    I refer back to my original suspicions regarding the fuel shut off solenoid - although as ccawgc suggests, it's likely a stuck valve internal to the carburetor and not an electrical issue but hey, I would have been in the right area.

    From your troubleshooting and testing results, the RUN circuit is working as it should by getting power downstream of the OP switch in START and RUN once the OP switch closes with oil pressure.

    My slightly older Bobcat 225G Plus doesn't "click" or "snap" in the RUN position and I don't see anything in the wiring diagram for your machine that would do so either so I can't explain that unless the idler solenoid normally activates momemtarily as the ingnition switch passes thru the RUN/IDLE position with the unit off and no power to Idler module pin 'B'. ?? Your unit ignition/idler control circuits differ only in that your Idler module uses 5 of 5 terminals and mine uses only 4 out of its 5 so they may function slightly different upon start-up.
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    WC-1S/Spoolmatic 1
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    Star Jet 21-110

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  6. #6
    Join Date
    Jul 2010
    Location
    NE North Carolina
    Posts
    3

    Re: Need Help!! Miller 250 NT crank NO start

    Guys, I thank you very much for the info!
    I have been sick for about a week and have not felt like any follow up. I started feeling bad and buttoned up the welder, not really doing anything else to it except pluging conections back in, installing covers etc. I did not even clean the carb, I was going to move it to the side and work on it later, but I decided to give it another try. Guess what IT STARTED!!! and runs like a dream. I do not have any idea unless something was not connected well or correded.... go figure anyhow I guess I took a class in diagnosing Miller welders. Again Thanks.

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