2002 Kubota STa 35 - Not starting but turns over

[biffo]

I am British based in France, my descriptions may not always use the correct terms but please bear with me.

We have had this tractor for about 15 years, never missed a beat or showed any malfunction of any part of it, I service it correctly at all times. A front bucket is fitted and a 4 feet flail mower is on the rear. It is used all year round to do something.

Started it (instant as usual), drove from the barn to a field about 200 yards away, everything working as always. Switched off, had to do something with a tree then 2-3 minutes later got back on. Engine turns over, makes the first sound of starting then nothing. Ok, try again, same thing happens.
Manage to tow the tractor back to near the barn and leave it there for a week while I try every day to start it after looking at various minor parts of the mechanicals. Each time it turns over, sputters for the first catch of the motor, then nothing.
There is fuel, I check each fuse, check the continuity of each fuse holder. I do this as although I know close to nothing about diesel engines I do know about gas (petrol) engines and how electrics can affect them. I notice the injectors are supplied with fuel from an assembly beside the engine block, and that (I confirmed later) there is a solenoid at one end which operates a plunger inside this assembly to switch fuel flow on and off. I am not sure if the solenoid could be the cause as I can't hear or feel it click each time we try to start it.

That this problem started without any prior warning at all, that it happened suddenly after running and driving perfectly for a few minutes made me think of electrical problem, it was as though a switch had been turned off or a fuse had blown (fuses all good).

Since this happened about 3 months ago I have travelled abroad twice (once to the US for 7 weeks) so haven't had much oportunity to look at the tractor, but we desparately need to get our 5 acres ready for winter and miss it badly.

Sorry it is such a lengthy story, any thoughts as to whether this is a known common problem or just a one off would be very much appreciated, thank you.

 

[thepumpguysc]

The “shut off” solenoid could definitely cause your problem..
Remove the push on wire connector and unscrew the solenoid..
U can bench test the solenoid by applying 12v to the connector and - to the body.. if the plunger retracts, it means u have a power supply issue..
If u REALLY NEED IT, put a piece of tape over the hole or stuff a small rag in it..
There is usually a manual shut off to the right of the throttle control linkages at the injection pump..
If not, you’ll have to stick your pinky finger in the solenoid hole to shut it down.. OR.. back out the low idle screw at the pump linkage to go past low idle and it will shut off..
Good luck

 

[JWR]

Does the engine continue to turn over as long as you want (with the starter) after it sputters each try? If it does I suspect some kind of fuel blockage. First thing to check is filters. Having had it 15 years you probably need to change the filters anyway unless recently done. I cannot remember if my Kubotas will turn with the shutoff enabled. I thought not. However thepumpguysc could be right.

 

[biffo]

Thanks a lot to you both, some very good information and a great deal to work with here.

We are having an unusual very wet year here this year, following 3 years or drought! The tractor is outside with 2 very heavy duty tarps tied down over it. We have rain predicted for the next week so 'probably' can't start work for a short while unless the forecast is wrong.
The barn is slightly uphill, not so big either so couldn't tow the tractor into the barn to work on, plus it is slightly uphill so difficult for the 2 of us to push.

JWR, the answer to your starter question is no.
Using the starter the engine turns over for maybe 2-3 seconds, the engine just begins to fire but only the very first moments of firing, maybe just a second, and then the starter stops immediately but the engine does not continue running, just stops immediately.
If I were to try to keep the starter turning it wouldn't, I would have to turn off and start the sequence again with the same result.

Is this pointing to a switch/cut-off/electrical problem aside or including the pump solenoid or just my wishful thinking?

I could try to hotwire the starter solenoid once I can get back to work on it, that would at least overide a switch or two wouldn't it?

Thank you both again

Edit: The start precedure has to include keeping the clutch pedal depressed.

 

[Robin Veerman]

All good ideas above, but how old is the battery? Is it turning over as fast as usual? Maybe have the battery load tested… if weak, replace it.

 

[biffo]

Thanks Robin, the battery is a good idea but that isn't the problem. It's 2 years old and the correct capacity for this tractor. I do keep day to day maintainance up to date to the point if we leave here for a week or longer I make sure I disconnect it.
I uncovered the tractor 2 days ago and immediately measured the voltage, it was 12.6v which after 3 1/2 months is pretty good seeing as when it broke down and I had to cover it up in a hurry I forgot to disconnect the Neg. lead.

When we pulled the tarps off last Saturday, I took another look around with fresh insight from suggestions here and my own ideas. After a short while we (my wife and I) started to get it ready to winch, tow and try to push the tractor into the barn, after we worked out how to raise the front bucket and rear flail mower. I was never going to work on it in the open with the wet weather we are still having all the time now along with colder than usual temperatures.

I thought for no logical reason to try to see if something had happened in the time it had been sitting on damp grass, so turned the ignition key. The glow plugs came on but didn't go off after the usual X seconds, just stayed on while the key was in the intermediate position. After about 30-40 seconds I tried to start it, it started as always before, instantly!
I immediately raised the flail mower and bucket off the ground, then after about 20 seconds it just stopped as though I had turned it off, but I hadn't.

First sat there thinking how lucky it was to think to get the equipment off the ground (I am not usually that sharp), and of course puzzled. Started to think if it started again for 20 seconds how could I line it up with the door of the barn in another short burst of running time, so tried again. Same glow plugs staying alight (until the motor starts) then started again! This time for about 40 seconds. Quickly adjusted the mower and bucket for pefect height to enter the barn and maneuvered the tractor into position then started to reverse in, it stopped again in the same manner.

I have to be precise on driving through the barn door as due to the bucket and mower I have about 3" each side and I have to enter at an angle, so no full throttle. Gave it a couple of minutes, checked the tractor parking space then tried to start again, exactly the same as before, instantly. Reversed in, positioned it in the best place to work on it from both sides and the motor continued running, it ran for about another 15 minutes until I turned it off. About 20 minutes later I went to start it again and it started, puzzled is an understatement.

Back to the battery. That it started the engine easily after 3 1/2 months was pleasing, and using the glow plugs much longer than the about 3-5 seconds it usually is.

When operating it all the controls and reactions of the tractor and equipment were exactly as they have been since I owned it, faultless.

Of course the problem can start all over again if I don't find the cause, so locating the fault is a must, it has to be found. But finding the cause when the problem has disappeared is every mechanic's nightmare.

I am very very lucky getting this into the barn late on Saturday afternoon, 30 minutes later it started to snow, heavily for here, which turned into ice rain.

I would be grateful for any more suggestions however improbable. To me this feels as though it is electrical, a connection being made and then disconnected. Not that I know much about diesel agricultural equipment.

Thank you everybody for your help, a happy and pleasant 2025 to all.


Edit: I may get a day or so at the start of January to start checking out switches and wiring, then lucky us we off travelling again for 5 weeks as we are now retired. When back I'll have more time to work on the tractor.

 

[JWR]

I still think it is a fuel issue. Suggest that you disconnect the fuel line as close to the injection pump as possible. See if you can get fuel flow out of the open line there. I'm guessing you will have just a small momentary fuel flow and then none while cranking or with the key in the Start position. Next I would use the equivalent of a medical IV drip bag -- any thing you can put together that provides a gravity feed of fuel to the injection pump. If the problem is fuel flow related you will be able to run the engine fed by a drip bag of fuel and then work your way back toward the tank to see what has been stopping fuel flow.
If my suspicion is correct, you are getting just enough fuel very slowly building up at the input to the injection pump to run the engine for a very short time only. Waiting a few minutes allows that same small of fuel to build up again so that you can repeat the exercise but no real continuous flow.

On a tractor more than 15 years old there are all sort of possibilities such as air leaks in the fuel tubing, accumulated debris making its way down from the fuel tank to the filters and clogging things at almost any location, etc.

 

[thepumpguysc]

I agree.^^
I’m thinking fuel is bleeding back to the tank after sitting.
U could plumb in an electric supply pump.. no more than 10 psi.. pull from the tank and push it to the inj pump.

 

[biffo]

I'll take all that on board, good advice for someone who hasn't ever worked with diesel or injection systems.

The one part that still puzzles though is with gas/petrol engined cars with carburettors a partial or intermittent fuel line blockage the engine does not stop suddenly but just sort of putters to a stop. When this motor stops it is sharp like flicking an electrical switch.

I'm here to learn, thank you again.

 

[Harry in Ky]

Reading all this tells me it's NOT a fuel issue, but electrical. A fuel issue may cause it to not start, yes, but the "start instantly", stop for no apparent reason, then start again "instantly" just just doesn't happen with fuel supply problems. It would require bleeding somewhere at some point. You need to revisit the shut off solenoid and/or the power supply to it. Don't start messing with filters, and/or fuel lines just yet as you will most likely introduce problems you don't yet have.