Kubota KX41 revs dropping when hydraulics are activated

[Godhungry777]

See video explanation.
Revs drop from 3000RPM to 1800RPM when any hydraulics are activated.

Any thoughts?

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) - had injector pump and 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
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

 

[K5lwq]

What happens when you move the controls at idle? Or lower RPMs? Then what happens when you dig or put a load on the hydraulics? Maybe even holding the valve open when cylinder bottoms out?

 

[oldnslo]

Do you have a hydraulic schematic for this machine?

Have you installed a pressure gauge on the pump pressure line?

Parts list indicate this model has fixed displacement gear pump or pumps depending on features. There should be minimal pressure with no functions be operated.

 

[JWR]

How many hours on the machine? I may have missed it if you said. Does the engine slow down or bog down when you move the machine around using the tracks ?

 

[Godhungry777]

How many hours on the machine? I may have missed it if you said. Does the engine slow down or bog down when you move the machine around using the tracks ?

4000 hours

Yes it does the same with driving the tracks. Everything is driven by the hydraulics so i don't really have a way of testing hydraulic load against any other type of load.

 

[Godhungry777]

Do you have a hydraulic schematic for this machine?

Have you installed a pressure gauge on the pump pressure line?

Parts list indicate this model has fixed displacement gear pump or pumps depending on features. There should be minimal pressure with no functions be operated.

Here's the schematic.
I don't have a pressure gauge.

 

[JWR]

4000 hours

Yes it does the same with driving the tracks. Everything is driven by the hydraulics so i don't really have a way of testing hydraulic load against any other type of load.

I am NOT experienced in this specific machine at all, BUT with 4000 hours on it and much of the overall operation of it using hydraulic pressure, I would have to guess your hydraulic pump is worn out.

Not sure how to test it but there must be others out there with high hours on one of these machines. The regional service rep for [AFFILIATE=1, nofollow=true, newwindow=true, title="Kubota"]Kubota[/AFFILIATE] (assuming they have those down under) should be able to comment and help you at least verbally on this... and that is his job. If it is a worn out central major part of that machine -- apparently is -- this is going to be expensive to replace it. Finding a shop that has done it before is likely to be your hardest search (and that won't be the local dealer who has never done it before...)

 

[oldnslo]

I am NOT experienced in this specific machine at all, BUT with 4000 hours on it and much of the overall operation of it using hydraulic pressure, I would have to guess your hydraulic pump is worn out.

JW
How would a worn pump cause the engine to slow down in RPM? Hydraulic function slower yes but engine ??

 

[oldnslo]

GodHungry
The schematic also shows your machine having fixed displacement pumps so unlikely the engine gradually slowing down is a hydraulic problem but I could be 100% wrong.

To confirm you need to have equipment to check system pressures or disconnect pumps from engine. This would 100% isolate engine from hydraulics. Most likely this is not feasible.

 

[Jerry/MT]

See video explanation.
Revs drop from 3000RPM to 1800RPM when any hydraulics are activated.

Any thoughts?

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) - had injector pump and 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
• cleaned and flushed hydraulic tank, replaced both filters (both filters were very clogged), filled with new oil.

Something is putting a big load on the engine via the hydraulics. Are the track drive bearings frozen, the brakes stuck ON, etc ?

 

[JWR]

JW
How would a worn pump cause the engine to slow down in RPM? Hydraulic function slower yes but engine ??

My thought is that a heavily loaded hydraulic pump could very well show high wear at 4000 hours. It seems plausible that the pump internal mechanism friction/drag increases as it wears and eventually that becomes significant drag on the motor driving it. That drag would logically increase as the hydraulic power output of the pump increases , thus loading down your engine. Power Out = Power In minus losses. I think you probably have increased losses due to wear but -- hey that is little more than an old engineer's educated guess... BUT I AM NO HYD PUMP EXPERT. You should find someone who knows the type of pump, whether these symptoms have been seen before and how to test for the disease.

To me it is likely, because I see no other way for activating your bucket or the tracks to load down the engine since you said all that is hydraulically driven. So clearly something besides normal working loads are loading down the pump and thus the engine. I suppose it is also possible that an obstruction in the valves or lines could load down the pump and thus the engine but that seems far fetched to me.

Another stray thought: You must have a governor on that engine. Normally when faced with increased load (e.g. normal demand from the hydraulic pump when you are using hydraulic power) the governor would increase fuel to the engine boosting rpm upward and avoiding dropping rpm. That's what a governor does. MAYBE you have some problem with the governor? Linkage maybe ?

One thing you failed to tell us: Did this problem come on very gradually over time or did it suddenly happen? That may offer a useful clue.

 

[K5lwq]

My thought is that a heavily loaded hydraulic pump could very well show high wear at 4000 hours. It seems plausible that the pump internal mechanism friction/drag increases as it wears and eventually that becomes significant drag on the motor driving it. That drag would logically increase as the hydraulic power output of the pump increases , thus loading down your engine. Power Out = Power In minus losses. I think you probably have increased losses due to wear but -- hey that is little more than an old engineer's educated guess... BUT I AM NO HYD PUMP EXPERT. You should find someone who knows the type of pump, whether these symptoms have been seen before and how to test for the disease.

To me it is likely, because I see no other way for activating your bucket or the tracks to load down the engine since you said all that is hydraulically driven. So clearly something besides normal working loads are loading down the pump and thus the engine. I suppose it is also possible that an obstruction in the valves or lines could load down the pump and thus the engine but that seems far fetched to me.

Another stray thought: You must have a governor on that engine. Normally when faced with increased load (e.g. normal demand from the hydraulic pump when you are using hydraulic power) the governor would increase fuel to the engine boosting rpm upward and avoiding dropping rpm. That's what a governor does. MAYBE you have some problem with the governor? Linkage maybe ?

One thing you failed to tell us: Did this problem come on very gradually over time or did it suddenly happen? That may offer a useful clue.

I was thinking governor as well. Another thought is does this unit have a ECM? I understand it is lower horsepower but it acts like something else is controlling engine speed other than linkage.

I would like to know what happens at a lower RPM and under a load. If it drops RPM the same amount or kills the engine I would think issue could be with Hydraulics and would be using a pressure gauge to confirm.

 

[oldnslo]

JWR,
By design gear pumps have clearances designed to allow some leakage past sides of gears to lube the plain bearings on the shaft. If these clearances change so leakage is reduced my experience is they typically seize if the friction gets high enough to load the engine.

Like K5 says we need more information on pressures, is this mechanical throttle and governor or electric.

I have significant hearing loss but to me it did not sound like that engine was struggling to maintain RPM from being over loaded. It just seemed like kind of dropped off slowly and recovered slowly.

 

[5030]

Slowly' usually indicates a fuel or filter issue.

 

[JWR]

JWR,
By design gear pumps have clearances designed to allow some leakage past sides of gears to lube the plain bearings on the shaft. If these clearances change so leakage is reduced my experience is they typically seize if the friction gets high enough to load the engine.

Like K5 says we need more information on pressures, is this mechanical throttle and governor or electric.

I have significant hearing loss but to me it did not sound like that engine was struggling to maintain RPM from being over loaded. It just seemed like kind of dropped off slowly and recovered slowly.

Yeah, so one wonders if his is about ready to seize ?

 

[oldnslo]

Yeah, so one wonders if his is about ready to seize ?

My guess is no. My experience there is very, very little time between about to and seized. This experience is from R & D testing at gear pump manufacturer.

 

[Fixastuff]

I'm thinking fuel delivery or governor problem based on the sound.

 

[Godhungry777]

What happens when you move the controls at idle? Or lower RPMs? Then what happens when you dig or put a load on the hydraulics? Maybe even holding the valve open when cylinder bottoms out?

I'm thinking fuel delivery or governor problem based on the sound.

Here's my thread chasing it as a fuel/governor issue Kubota 05 Series Engine - Bogging Under Load, Loses Power When Warm (Kubota KX41 - D1105 Engine)

The throttle slide on the Injector Pump is free and all governor linkages are free and move the slider. You'll see the governor move the slider at startup in the video here but not move it when load is added. I guess there's a possibility that the hydraulic load already has the governor maxed out and any further load is too much and drags the RPM down.

 

[Godhungry777]

I was thinking governor as well. Another thought is does this unit have a ECM? I understand it is lower horsepower but it acts like something else is controlling engine speed other than linkage.

I would like to know what happens at a lower RPM and under a load. If it drops RPM the same amount or kills the engine I would think issue could be with Hydraulics and would be using a pressure gauge to confirm.

OK. So yes it's very different at lower RPM.
At 1500RPM there is very little drop - drops to 1400 under the heaviest load.
At 2000 RPM it drops to 1800ish.
I'm guessing that this would point us back to fuel rather than hydraulics? Or not necessarily if higher throughput of oil in hydraulics at higher RPM amplifies the effect of any blockage/restriction in hydraulic system?

 

[Jerry/MT]

Look

K. So yes it's very different at lower RPM.
At 1500RPM there is very little drop - drops to 1400 under the heaviest load.
At 2000 RPM it drops to 1800ish.
I'm guessing that this would point us back to fuel rather than hydraulics? Or not necessarily if higher throughput of oil in hydraulics at higher RPM amplifies the effect of any blockage/restriction in hydraulic system?

Look at my comment at the Orange Tractor Talk Forum. The load that you are putting on the machine by curling the bucket is very small, so I think your problem is fuel flow related. Remove the line that goes to the Injector Pump. Crank the engine and you should have a steady full stream of fuel from that line. If it dribbles, is intermittent, and is not a full stream, check the lift pump and the filter head as well as the tank outlet. If you had a dirty fuel tank, you might not have gotten all the crap and corruption out of the system.