Kubota kx41 stalling problem

[GRIFFO]

Hi I have a kubota kx41 .
when operating any hydraulic controls at low - medium revs it causes the engine to stall
I thought this could be a fuel problem ( I recently changed the fuel filter ),
but could it be a hydraulic problem ?
any help appreciated !!

[Muz]

Maybe someone has upped the MRV's so the hydraulics are delivering higher pressures than they should, which will labour the engine more. So if your sure the engine is ok, a pressure test will reveal that. which model of 41 is it ?

[GRIFFO]

Maybe someone has upped the MRV's so the hydraulics are delivering higher pressures than they should, which will labour the engine more. So if your sure the engine is ok, a pressure test will reveal that. which model of 41 is it ?

It's a KX41-3

[GRIFFO]

It's a KX41-3

It's a 2 speed with track adjustable tracks

[Muz]

IIRC it will be a variable displacement pump on that then is it ? If so .. could be that its stuck on full delivery. How many hours are on it ?

[GRIFFO]

IIRC it will be a variable displacement pump on that then is it ? If so .. could be that its stuck on full delivery. How many hours are on it ?

It does have a variable displacement pump ( according to the machine specs ) the machine hours are 3353.4
how would I go about freeing it up if it is stuck on ?
Also the tracks & dozer blade are both slow to retract.

[Muz]

Well I don't know the pump architecture .. But if it's not a mechanical failure of the pump, some of them have an 'unloader' valve on the pump that returns the swash plate to zero when you turn the digger off. If that valve is stuck, it leaves the plate stuck full on. It might be a valve physically on the pump. Is the machine hard to crank over on start up?

And I take it you've checked all the other obvious things such as stones caught under breaker pedals , or the breaker pedal isn't seized 'on' ?

[GRIFFO]

Well I don't know the pump architecture .. But if it's not a mechanical failure of the pump, some of them have an 'unloader' valve on the pump that returns the swash plate to zero when you turn the digger off. If that valve is stuck, it leaves the plate stuck full on. It might be a valve physically on the pump. Is the machine hard to crank over on start up?

The machine starts ok, but initially when the engine stalled (due to operating hydraulics) it would then be hard to start again,
this problem seems to have rectified itself since we changed the hydraulic oil & filter .
we checked the hyd pressure on all pumps and they seem to be right (216 bar ),

[Muz]

The machine starts ok, but initially when the engine stalled (due to operating hydraulics) it would then be hard to start again,
this problem seems to have rectified itself since we changed the hydraulic oil & filter .
we checked the hyd pressure on all pumps and they seem to be right (216 bar ),

Well the filters are on the return side, so they wouldnt usually cause your problem. Are you saying everything is good now ?

[GRIFFO]

Well the filters are on the return side, so they wouldnt usually cause your problem. Are you saying everything is good now ?

No the engine starts ok now but it still stalls when operating hydraulics on lower revs .

[Muz]

No the engine starts ok now but it still stalls when operating hydraulics on lower revs .

Its fair to say I have some diggers that also stall if I pull on some services when the machine is at idle, particularly when the oil is cold .. I have a u25 that will do this.

I take it youve checked the pedals and rockers are clear and unobstructed as I mentioned earlier ?

Whats the lowest position the throttle is at to keep the digger running ?

And it does this when its hot as well as cold ?

[GRIFFO]

Its fair to say I have some diggers that also stall if I pull on some services when the machine is at idle, particularly when the oil is cold .. I have a u25 that will do this.

I take it youve checked the pedals and rockers are clear and unobstructed as I mentioned earlier ?

Whats the lowest position the throttle is at to keep the digger running ?

And it does this when its hot as well as cold ?

I have checked all rockers & pedals all seems to be clear
it does the same hot or cold & stalls about half throttle when I pull the boom fully closed.
When on full throttle you can pull both the boom & arm fully in without stalling.
Also when tracking it will stall just below half throttle.

[Muz]

I have checked all rockers & pedals all seems to be clear
it does the same hot or cold & stalls about half throttle when I pull the boom fully closed.
When on full throttle you can pull both the boom & arm fully in without stalling.
Also when tracking it will stall just below half throttle.

Back to my first reply then .. my Volvo EC15's run at 190 Bar , so yours is nearly 30 Bar over that, so someone might have opened the relief valves too much, that said, I dont know what the 41 is supposed to run at, you'd need to check the correct pressure from a dealer.

Does the engine produce black smoke at full revs when under load ?

Also .. although the pedals are clear, are they centered properly ?

[GRIFFO]

Back to my first reply then .. my Volvo EC15's run at 190 Bar , so yours is nearly 30 Bar over that, so someone might have opened the relief valves too much, that said, I dont know what the 41 is supposed to run at, you'd need to check the correct pressure from a dealer.

Does the engine produce black smoke at full revs when under load ?

Also .. although the pedals are clear, are they centered properly ?

Have checked all the pedals etc And they are all ok not stuck open,

the engine doesn't produce any smoke under load.

have checked the pressures again and although they are within spec the pressure on the dozer blade when retracting is low
same with the tracks when retracting .

[Muz]

If everything else is ok, I keep coming back to a main relief valve problem. One thing you might like to try is to put your pressure tester 'in line' with the boom lift circuit. As you gradually pull on the service, you should gradually see the pressure gauge rise, but in your case it sounds as if its going from 0 - 230 bar instantly ? .. try that and see what happens ? .. thereafter it might be a case of swapping them about to see if you can replicate it on another circuit such as the dipper ram, which will be on a different circuit