Kubota KX41 revs dropping when hydraulics are activated

[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.