Kubota KX41 revs dropping when hydraulics are activated

[Jerry/MT]

Does this machine only have one pump? I thought the schematic showed 3 separate pumps P1, P2, and P3.

It did not look like unstable rpm's to me from the video. I'll take your word for it that it is. That would point to a problem with the governor in the IP since you supposedly have the hydraulics disconnected.

 

[Godhungry777]

Does this machine only have one pump? I thought the schematic showed 3 separate pumps P1, P2, and P3.

It did not look like unstable rpm's to me from the video. I'll take your word for it that it is. That would point to a problem with the governor in the IP since you supposedly have the hydraulics disconnected.

3in1

Instability is probably the wrong description. You're right that it's stable once it reaches the throttle setting. What I'm referring to is that when you set the throttle, it takes so long for the revs to get up or down to where you've set it that you need to keep make adjustments once it gets there to try get it to set at 2300RPM.
A good chunk of the 2 minute video is me adjusting the throttle just trying to get it to 2300RPM.

 

[K5lwq]

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.

There is a sharp guy on this forum that goes by @thepumpguysc. I think he may have some suggestions if he sees this thread.

 

[ddbackhoe]

There is a sharp guy on this forum that goes by @thepumpguysc. I think he may have some suggestions if he sees this thread.

I was wondering why he had not chimed in. Wouldn't hurt to pm him.

 

[number two]

TBN has been down a lot for me this week.

 

[thepumpguysc]

Thanks for thinking about me..
We’ve chatted about this on another forum..with no improvement, sorry to say..

 

[ddbackhoe]

Thanks for thinking about me..
We’ve chatted about this on another forum..with no improvement, sorry to say..

Well, whats left? If fuel delivery is ok, timing is good, valve lash is ok….My next thought would be to use an endoscope camera to look at piston walls, valves and valve seats. Other guesses?

Links posted for suggestions only. Your usage may vary

https://www.amazon.com/Endoscope-Borescope-Inspection-Waterproof-Semi-Rigid/dp/B09NVYXTG5

 

[thepumpguysc]

I don’t think the pump has been apart and put back together by a “qualified” inj pump tech.??
He also has the max fuel and torque screw completely out.. there’s no starting point..
It’s my “guess” is, that between the rpm’s and max fuel, he’s overcoming the gov springs with any load applied..
It’s just a guess mind you..

 

[aesmith]

What strikes me is how slow that engine revs up. Something like 40 seconds or so from when he let go of the throttle until the revs stopped rising? We have the same machine, KX41 with D1105BH engine. I'm sure it doesn't take more than a second or so, maybe even less to rev up when I adjust the throttle.

 

[hayden]

It's definitely the governor. I don't know how it works on that particular engine, but no governing is happening.

 

[hayden]

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.

I don't think this video really tells you anything. It just shows the injection cam rotating, but we already know that because the engine is running. I think you will need to get the manual for the injection pump and see how the governor works.

 

[thepumpguysc]

U can get a kubota engine manual and it shows all the pre-sets..

 

[K5lwq]

What strikes me is how slow that engine revs up. Something like 40 seconds or so from when he let go of the throttle until the revs stopped rising? We have the same machine, KX41 with D1105BH engine. I'm sure it doesn't take more than a second or so, maybe even less to rev up when I adjust the throttle.

I would be interested in what your RPM is at its highest throttle position? I still think someone tried to turn the power up on the OPs machine and did not understand what they were doing.

 

[thepumpguysc]

The max fuel screw has another screw adjuster in it..
it’s the torque screw..
When u turn one up, (add more fuel) to which u actually BACK OUT the screw, u should only turn the whole assembly..
That way u turn the fuel proportionally.. fuel goes up, torque goes up ..
It would make sense that ur correct.. On A LOT of systems, the max adjuster gets turned IN..

 

[5030]

U can get a kubota engine manual and it shows all the pre-sets..

Online as well at Kubotabooks.net. Had my dealer crank both of mine up a few years ago. One is making 93 pto, the other is at 91. Hard to match them perfectly. No impact in gallons per hour used either. M9's are supposed to be factory set at 83-85.

 

[aesmith]

Here's mine for comparison, just opening and closing throttle. A bit "boomy" at idle because the engine cover is up. Rev counter doesn't work but hopefully the engine noise is enough to make the point.

 

[Godhungry777]

Here's mine for comparison, just opening and closing throttle. A bit "boomy" at idle because the engine cover is up. Rev counter doesn't work but hopefully the engine noise is enough to make the point.

Thanks heaps for that. Yes that is a vast difference.

 

[Godhungry777]

I don’t think the pump has been apart and put back together by a “qualified” inj pump tech.??
He also has the max fuel and torque screw completely out.. there’s no starting point..
It’s my “guess” is, that between the rpm’s and max fuel, he’s overcoming the gov springs with any load applied..
It’s just a guess mind you..

The IP has now been professionally rebuilt and recalibrated by our local Bosch injector/pump specialist.
No change to symptoms.

 

[Godhungry777]

UPDATE

My apologies to all for the delay. It has taken me forever to get hold of a Diesel Compression Tester with the adapters i needed.

So to update:
INJECTOR PUMP > I got the Injector Pump professionally rebuilt and calibrated by our local Bosch injector/pump specialist - no change to over revving, lack of power and bogging under load.

COMPRESSION TEST >
The manual says compression should be 412-469 PSI (Rebuild under 327 PSI)
My results:
Cylinder 1 - 380PSI
Cylinder 2 - 410PSI
Cylinder 3 - 320PSI

So all are below operating range and one below rebuild indicator.

Is low compression also going to cause the slow RPM response to throttle movement?
Or are there still other issues (eg governor) that I'm dealing with for that?

 

[K5lwq]

UPDATE

My apologies to all for the delay. It has taken me forever to get hold of a Diesel Compression Tester with the adapters i needed.

So to update:
INJECTOR PUMP > I got the Injector Pump professionally rebuilt and calibrated by our local Bosch injector/pump specialist - no change to over revving, lack of power and bogging under load.

COMPRESSION TEST >
The manual says compression should be 412-469 PSI (Rebuild under 327 PSI)
My results:
Cylinder 1 - 380PSI
Cylinder 2 - 410PSI
Cylinder 3 - 320PSI

So all are below operating range and one below rebuild indicator.

Is low compression also going to cause the slow RPM response to throttle movement?
Or are there still other issues (eg governor) that I'm dealing with for that?

I do not see how low compression could cause the slow throttle response or the high RPM. It would possibly explain a slight loss in power with those numbers but should still be usable.

I would still think governor or the fuel torque still out of adjustment. If it were my unit I would set the RPM to 1500 to 1800 and work it. Even if you did the rebuild I think this problem would still exist.