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Thread: diesel diagnosis

  1. #1
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    Default diesel diagnosis

    my lil kubota is running fine but needs the starter held for too long to catch fire. it will sound like it is running but releasing the starter normally causes abrupt silence. a little bump of fuel pedal helps. and yes i know that's bad operator behavior. seems to run fine without perceptible (to me) power loss (could be wrong about that), no stalling. i have recently changed the fuel and air filters.

    long term, my temp gauge registers some heat but has never got to the operating range. i changed the thermostat, no difference. over time, tractor has smoked more at start up, but is not smoking otherwise.

    i wonder if my symptoms could be coking up of the cylinders from operating too cold? or if it is more likely a fueling problem. any wisdom appreciated.

  2. #2
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    Default Re: diesel diagnosis

    glow plugs working?

    instead of running the starter try this:
    turn ignition to on
    after glow plug light goes out bump the start for about two seconds to get some fresh fuel into the cylinders
    then push the button to reheat the glow plugs manually four about four seconds
    then hit the starter

    this will help on cold and wet days

    a little extra fuel (throttle) is not bad, say revved to 950 instead of 750 during ignition

    and yes these little high speed diesel engines need a bit of heat in them to stay running at their best
    Last edited by Paul Pless; 12-27-2020 at 10:01 AM.
    Simpler is better, except when complicated looks really cool.

  3. #3
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    Default Re: diesel diagnosis

    the problem is identical on warm start up. i don't know how to check glow plugs.

    eta: i can google, tho. looks like i can manage a glow plug test

  4. #4
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    Default Re: diesel diagnosis

    My DuraMax blue a good cloud of raw fuel yesterday. Hadn't been started in a week. Do you use Power Service additives?
    The 911 anti gel is a must here.
    Tom

  5. #5
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    Default Re: diesel diagnosis

    if its happening on warm start its not the glow plugs

    fuel, fuel filter, water separator, fuel injection pump (unlikely and complicated)

    first thing i would check this time of year is how much water is in the fuel/water separator cup - it has a drain at the bottom for checking this - also when not used often, meaning not often enough to burn a tank of fuel every week or so, your fuel tank itself may develop condensation issues

    keep your tank full of fresh fuel to prevent room for condensation and even if you don't need to run the tractor weekly fir an hour at moderate rpm and temp range

    use a fuel treatment additive
    Simpler is better, except when complicated looks really cool.

  6. #6
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    Default Re: diesel diagnosis

    here's something: there is no perceptible noise when i key the glow plugs, and the indicator light doesn't go out, even after a long eight count. i've never seen that light go out while allegedly warming the plugs. just reckoned that was a feature of this particular beast.

    can glow plugs be silent? every other diesel i've run had a little noise accompanying the glow plugs.

    i wonder if the glow plugs have never been functional, and i've just been compression starting all along.

  7. #7
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    Default Re: diesel diagnosis

    Quote Originally Posted by Tom from Rubicon View Post
    My DuraMax blue a good cloud of raw fuel yesterday. Hadn't been started in a week. Do you use Power Service additives?
    The 911 anti gel is a must here.
    Tom
    don't use any additives, but it barely gets below freezing here. coldest start has been low thirties. my '06 powersmoke will also blow a cloud after a layoff and temps below 40f.

  8. #8
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    Default Re: diesel diagnosis

    check the glow plug relay in the fuse box, you might havd an identical relay fir something like the pto clutch you swap it with to see if that works - those kubota relays are inordinately expensive f***ers, they are better purchased at napa than at the kubota store
    Last edited by Paul Pless; 12-27-2020 at 10:20 AM.
    Simpler is better, except when complicated looks really cool.

  9. #9
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    Default Re: diesel diagnosis

    One thing I would be looking at a bit closely , if I had a tractor, which I don't because sometimes life is unfair, is the stop circuit.
    Ie ifn it was old the stop cable adjustment and if it was new just make sure the solenoid was correctly adjusted, spring stiĺl present etc.

  10. #10
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    Default Re: diesel diagnosis

    Quote Originally Posted by John B View Post
    One thing I would be looking at a bit closely , if I had a tractor, which I don't because sometimes life is unfair, is the stop circuit.
    Ie ifn it was old the stop cable adjustment and if it was new just make sure the solenoid was correctly adjusted, spring stiĺl present etc.
    Are we talking 'compression release valve'?

    'Cause that's what I was thinking.

    If the machine has such a valve/system, and the works got a little dirty, it may not be developing enough compression to do the trick.

    And now I've told y'all more than I actually know about Diesels.

  11. #11
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    Default Re: diesel diagnosis

    no compression release on modern kubota tractors
    Simpler is better, except when complicated looks really cool.

  12. #12
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    Default Re: diesel diagnosis

    Check and clean the electrical connections to the glow plugs from the relay to the actual glow plug. If/when good, measure voltage at the glow-plugs and back to the relay to prove the relay/connections. (I wonder if the relay has a thermal time switch?) If good, remove the glowplugs and test on the bench for glowing. Even one defective glowplug will make it hard starting. The fact that it starts hard when warm sort of points in that direction.
    If none of the above indicates a problem I would suspect a compression problem, and prove that before I went much further.
    Fuel delivery is regulated by the governor. It should automatically default to WOT when cranking. Fooling with the throttle while cranking does nothing and will yield the exact same results as a red chicken running past the bucket at the exact moment you are cranking the starter.
    Diesels are temperature dependent, make sure the gauge is accurate and if so figure out why it is not coming up to temperature. A cold running diesel will have premature cylinder/ring wear.

  13. #13
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    Default Re: diesel diagnosis

    Quote Originally Posted by Canoeyawl View Post
    Check and clean the electrical connections to the glow plugs from the relay to the actual glow plug. If/when good, measure voltage at the glow-plugs and back to the relay to prove the relay/connections. (I wonder if the relay has a thermal time switch?) If good, remove the glowplugs and test on the bench for glowing. Even one defective glowplug will make it hard starting. The fact that it starts hard when warm sort of points in that direction.
    If none of the above indicates a problem I would suspect a compression problem, and prove that before I went much further.
    Fuel delivery is regulated by the governor. It should automatically default to WOT when cranking. Fooling with the throttle while cranking does nothing and will yield the exact same results as a red chicken running past the bucket at the exact moment you are cranking the starter.
    Diesels are temperature dependent, make sure the gauge is accurate and if so figure out why it is not coming up to temperature. A cold running diesel will have premature cylinder/ring wear.
    It's good to know that workaround. The red chicken thing is just too unpredictable.

  14. #14
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    Default Re: diesel diagnosis

    well, it's weird, because when i blip the throttle there is a noticeable kick up in the revs and it starts right up, i can let off the starter as normal. then again, the red chickens run past all the time so i dunno.

  15. #15
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    Default Re: diesel diagnosis

    I rang my diesel mechanic up as i thought there was water in the fuel of my Hyundai van. There was about 35 liters of diesel in the tank. His advice was to put a cup of metho in the tank as it acts as an emulsifier. Metho is mostly ethanol alcohol. On my boat the tank has a cone at the bottom of the cylinder tank and its easy to drain the water but not so in the Hyundai.
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  16. #16
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    Default Re: diesel diagnosis

    From atop my Everest of ignorance about Diesel engines in general, and Kubotas, in particular, does it have a lift pump for the fuel?

  17. #17
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    Cool Re: diesel diagnosis

    First you must cast the demons out.
    Until you do that, everything you do is pointless.
    Try cussin at it in Latin.
    Something like....."Mini tractores vos satus stultus"!!!!
    Keep calm, persistence beats resistance.

  18. #18
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    Default Re: diesel diagnosis


  19. #19
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    Default Re: diesel diagnosis

    Quote Originally Posted by Canoeyawl View Post
    Check and clean the electrical connections to the glow plugs from the relay to the actual glow plug. If/when good, measure voltage at the glow-plugs and back to the relay to prove the relay/connections. (I wonder if the relay has a thermal time switch?) If good, remove the glowplugs and test on the bench for glowing. Even one defective glowplug will make it hard starting. The fact that it starts hard when warm sort of points in that direction.
    If none of the above indicates a problem I would suspect a compression problem, and prove that before I went much further.
    Fuel delivery is regulated by the governor. It should automatically default to WOT when cranking. Fooling with the throttle while cranking does nothing and will yield the exact same results as a red chicken running past the bucket at the exact moment you are cranking the starter.
    Diesels are temperature dependent, make sure the gauge is accurate and if so figure out why it is not coming up to temperature. A cold running diesel will have premature cylinder/ring wear.
    If its a mechanical injector pump, I dont believe that is correct, at least not universally so. If its common rail, with electronic injectors, then it's all down to whatever the ECU does.

    Pete

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    Default

    You must chant, thusly.

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    Come ku-bota
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    Come ku-bota
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  21. #21
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    Default Re: diesel diagnosis

    Often the glow plugs are in series with a fuel lift pump or oil pressure pump. Either one of those would make the expected noise.

    If you're not intimate with your fuel filters yet....it's time to start an affair.

  22. #22
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    Default Re: diesel diagnosis

    to be clear, i am not struggling to start the tractor. i just need to hold the starter on for two or three seconds longer than normal, or blip the throttle with starter engaged and it will start. both of those conditions suggest there is something wrong, in my experience.

  23. #23
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    Default Re: diesel diagnosis

    Quote Originally Posted by David W Pratt View Post
    From atop my Everest of ignorance about Diesel engines in general, and Kubotas, in particular, does it have a lift pump for the fuel?
    That's a very good point. On my old medium duty truck that would sit for a long time, and had a long draw from the fuel tank to the injection pump, I put an inexpensive ($20 in 2004) low pressure electric fuel pump right on top of the fuel tank (fuel pumps push better than pull, you want a short pull), and, a brass stopcock valve right next to it, as double protection. The pump makes sure there is fuel supply at the engine at the moment of starting, and the stopcock prevents losing prime, i.e., all the fuel draining out of the line to the tank, and the injection pump trying to suck on air on a long pull.

    Starting: Connect electric fuel pump, open stopcock, follow normal engine start procedure. Once engine is started, I can actually disconnect electric fuel pump as the engine will draw fuel right through it.

    Shutting off: Turn off engine, close stopcock, disconnect electric fuel pump if still connected.

    Additional:

    - Water separator is critical to prevent damage to the fuel injectors by the water.

    - A diesel engine start/stop circuit is a solenoid valve that opens or shuts off fuel flow to the engine. My engine would start on starting fluid and then immediately die. The solenoid valve was bad, not opening, so no fuel.

    - The engine needs sufficient compression for the air in the cylinders to exceed the ignition temperature of the fuel. (NOT flash point, which is the spark ignition temperature.) This is a compression-ignition engine, not a spark-ignition engine. Heating the engine in any way helps; glow plugs, intake air heater, flame intake heater (military), hot air gun in intake (as long as everything downstream is heat safe so not plastic, and if so, just very careful warm air at the intake, not hot). But if engine compression gets too low, it's not going to start.

    - Certain additives to the fuel will help starting; Even if not cold enough for wax particles to form in the fuel, some additives will raise the cetane rating, making the fuel light off at a lower ignition temperature. Be careful, some additives will lower the cetane rating. For example, gasoline actually has a higher ignition temperature than diesel fuel, and the engine will not start, unless it is a "multi-fuel" engine which has a MASSIVE compression ratio exceeding that of even diesels. A guy I used to work with, he posted online a pic of him in Europe, having rented an Audi A8 diesel and accidentally putting gasoline in the tank, the pic is from him at the mechanic, them draining out the gasoline.
    Last edited by Bob (oh, THAT Bob); 12-27-2020 at 07:30 PM.
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  24. #24
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    Default Re: diesel diagnosis

    Does it blow white smoke when turning over, prior to start up?
    No smoke is no fuel. White smoke is not enough heat.

    Did the behaviour change after doing the fuel filter?
    Maybe try bleeding it again. A wee bubble might not stop it from running,but the pump relies on solid fuel to operate the injectors and it might take a second or two more to compress the bubble while cranking.

    R
    Sleep with one eye open.

  25. #25
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    Default Re: diesel diagnosis

    I used to have a Mercedes 300CD turbo and I learned a lot about diesels.

    What was mentioned about the fuel filter...start there. Changing the fuel filter on a diesel is very different than a gas engine. First the filter it way bigger, second it needs to be replaced more often and third you have to re-prime the fuel system after you replace the filter. Get the manual, the parts, your tools and have at it.

    Occam's Razor for diesels...always check the fuel. Also beware that if you ever have a small air leak in the fuel system, the engine will not run. Re-priming the systems on my MB 300CD and my Yanmar were both very straight forward.

    If you can start by hitting the gas a little...seems like it just might be your fuel system.

    Russell
    Last edited by rregge; 12-27-2020 at 11:25 PM.

  26. #26
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    Default Re: diesel diagnosis

    just out of curiosity, how long does the fuel sit in your tank between needing to refuel?
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  27. #27
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    Default Re: diesel diagnosis

    Quote Originally Posted by L.W. Baxter View Post
    to be clear, i am not struggling to start the tractor. i just need to hold the starter on for two or three seconds longer than normal, .
    What is "normal"? What does the manual say? Some old Nuffields or Perkins had to have pre heat for a minimum of 40 seconds before turning the key. A voltage test on your glow plugs would be worthwhile.

  28. #28
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    Default Re: diesel diagnosis

    On my little Kubota (2002 BX1800), the glow plugs are not on a timer - they stay on for as long as you hold the key in the correct position. Glow plugs make no noise - as they are simply a heating element inside the head. My tractor has an electric fuel pump which you can hear clicking while heating the plugs, but that just comes on when the key is on. Also - cracking the throttle to 900RPM or so makes it start far more easily - hot or cold.
    "If it ain't broke, you're not trying." - Red Green

  29. #29
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    Default Re: diesel diagnosis

    Did you bleed all the air out of the fuel line after you changed the fuel filter?

    On the Farymann on board Drake I had to make up a bleed-er using the squeeze-bulb from an outboard motor, and appropriate hoses and nipples. It is the only way to get the fuel filter can full of fuel again after a filter change.

    Dave

  30. #30
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    Default Re: diesel diagnosis

    Also, check the seal/gasket of the fuel filter canister. I don't know if yours is under pressure or vacuum, but make sure you haven't got a piece of crap messing up the gasket.

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