Kubota KX41 revs dropping when hydraulics are activated

[Godhungry777]

The vast majority of stalling issues are caused by fuel starvation. Does the engine blow black smoke or otherwise act like it’s working hard when it’s slowing?

No smoke of any colour at any point.

See video here

 

[ddbackhoe]

No smoke of any colour at any point.

See video here

At this point, I would look to separate into 2 halves, engine and hydraulics. Maybe not a fuel issue but a power coupling problem. How is the engine coupled to the hydraulic system? flex plate or?

 

[oldnslo]

Thanks for reposting the schematic

In reviewing the schematic from post #29 I noticed in lower left corner all of the pump flows were stated for 2,400 RPM. Not sure if that would say the engine on this machine should be at 2,400 RPM or not.

Pump 1 &2: 13.2 liters/min @ 195 Bar
Pump 3: 9.8 liters/min @ 210 Bar

This is a triple pump system. Per schematic none of of the pumps can combine flow.
Pump 1 feeds right travel, boom and bucket functions
pump 2 feeds left travel, arm and if installed 3rd section for running breaker or other attachments.
pump 3 feeds swivel or rotate motor, swing cylinder and dozer blade

Based on this you would have to monitor three pressure points to insure the system is functioning correctly. If operating two functions from two different pumps like boom and arm simultaneously does engine slow down more or stall since this should now but a greater load on the engine?

 

[hayden]

The fact that the engine is over-reving in the first place, and loses RPM when any load is applied, really says that the governor isn't working. The governor should limit RPMs to 2600 (or whatever the design max is), and increase fuel in response to load to maintain RPM. Your engine is not doing either of those things. Bad governor.

 

[Godhungry777]

The fact that the engine is over-reving in the first place, and loses RPM when any load is applied, really says that the governor isn't working. The governor should limit RPMs to 2600 (or whatever the design max is), and increase fuel in response to load to maintain RPM. Your engine is not doing either of those things. Bad governor.

I agree (somewhat) but is it not working because it's faulty or because it's maxed out trying to compensate for an unusual hydraulic load?
I have had the governor out and while it is a bit worn, nothing is broken or missing and everything moves smoothly and freely - forks/fingers, flyweight, slider, etc.

 

[Fixastuff]

The engine does not sound like it's being dead headed to me and I think other people agree.

 

[K5lwq]

I am confident that the hydraulics are not the issue although if we knew pressures from the different pumps it would confirm. But the fact it acts somewhat normally at low RPM and the fact the engine is turning more RPMs than it should, shows there definitely is a problem with the engine. I would be trying to adjust that engine to it’s peak power curve that appears to be around 2300 RPM.

 

[Godhungry777]

Update: Uncoupled Hydraulic Motor

OK, I've uncoupled the hydraulic motor to remove any effect of the hydraulics on the revs.
See video.
In my introduction I say that uncoupling the motor had stabilised the revs but then my test on camera completely disproved that as the RPMs were all over the place.

• It still over-revs at even half throttle (WSM has Max Revs at 2400RPM)
• It still takes for ever to increase or decrease RPM when the throttle is adjusted.

So, while we may still have a hydraulic issue, I think we need to sort out this unstable RPM issue first.

Here's what I've done so far:

• emptied and cleaned fuel tank (had water, rust and gunk)
• replaced fuel filters (clogged with water and gunk from tank)
• replaced fuel lines (lines were brittle) -
• tested injector pump - pumping fuel evenly from all three pumps. Tested straight from outlets and through injectors.
• Tested fuel slider rail. Full and free movement.
• had injectors tested - tested ok
• bled injector lines
• replaced engine oil and oil filter
• replaced thermostat and coolant (thermostat was stuck open)
• air filter had already been replaced - exhaust is clear
• checked governor spring, forks and flyweight. Worn but nothing broken or missing. All free moving.
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

 

[ddbackhoe]

injection pump, injection pump timing and valve lash are my 3 guesses at this point.

 

[Jerry/MT]

Update: Uncoupled Hydraulic Motor

OK, I've uncoupled the hydraulic motor to remove any effect of the hydraulics on the revs.
See video.
In my introduction I say that uncoupling the motor had stabilised the revs but then my test on camera completely disproved that as the RPMs were all over the place.

• It still over-revs at even half throttle (WSM has Max Revs at 2400RPM)
• It still takes for ever to increase or decrease RPM when the throttle is adjusted.

So, while we may still have a hydraulic issue, I think we need to sort out this unstable RPM issue first.

Here's what I've done so far:

• emptied and cleaned fuel tank (had water, rust and gunk)
• replaced fuel filters (clogged with water and gunk from tank)
• replaced fuel lines (lines were brittle) -
• tested injector pump - pumping fuel evenly from all three pumps. Tested straight from outlets and through injectors.
• Tested fuel slider rail. Full and free movement.
• had injectors tested - tested ok
• bled injector lines
• replaced engine oil and oil filter
• replaced thermostat and coolant (thermostat was stuck open)
• air filter had already been replaced - exhaust is clear
• checked governor spring, forks and flyweight. Worn but nothing broken or missing. All free moving.
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.