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.

 

[GreensvilleJay]

hour many hours on the engine ?
what is the compression of each cylinder ?

I've had gas engines start and run GREAT...purr like kick, responsive ... UNTIL put under a load, then they 'die'. every time ...they had 'weak' compression. One had 40#, ran 'fine' until loaded. Can't see a diesel being any different. I KNOW my BUDA BD153 will stall out under load.

 

[GodHungry777]

hour many hours on the engine ?
what is the compression of each cylinder ?

I've had gas engines start and run GREAT...purr like kick, responsive ... UNTIL put under a load, then they 'die'. every time ...they had 'weak' compression. One had 40#, ran 'fine' until loaded. Can't see a diesel being any different. I KNOW my BUDA BD153 will stall out under load.

4000 hours.
I don't have a diesel compression tester. I'll ask around. In the mean time, would there be any external indicators of low compression - eg. smoking under load?

 

[North Idaho Wolfman]

I was going to say you need to check the pressure relief valve.
But I'm also not liking the way the engine sounds, it does not sound like it's firing properly.

Nothing really externally on low compression.
I would also suggest that you do that before you invest more time and money in it.
Compression testers are cheap.

 

[GodHungry777]

I was going to say you need to check the pressure relief valve.
But I'm also not liking the way the engine sounds, it does not sound like it's firing properly.

Nothing really externally on low compression.
I would also suggest that you do that before you invest more time and money in it.
Compression testers are cheap.

Can you point me to anything that tells me how to check/test the relief valve?

I'll try find a second hand compression tester. The cheap ones start at about $300 and regular ones are about $700 here in Oz.

 

[North Idaho Wolfman]

Do you have the WSM?
It should be in there.

 

[mikester]

Do you have a diverter valve in the wrong position somewhere?

 

[GodHungry777]

Do you have the WSM?
It should be in there.

The 500 page, multi-language, $150 Kubota workshop manual is one of the most useless manuals I've ever bought.

 

[GodHungry777]

Do you have a diverter valve in the wrong position somewhere?

Is there another name for a diverter valve (see schematic attached)?

 

[JerryMT]

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.

Did you check the actual fuel flow to the injector pump? Since you had "...water and gunk..." in the tank, you might have crud in the head of the fuel filter that is restricting flow. If you have a lift pump, is it functioning properly?

I would disconnect the line at the line going to the Injector pump and crank the engine and look at the fuel stream coming out of that fuel line. ( if you have an electric fuel pump, turning on the key should activate it.) It should be a full stream, not intermittent or dribbling. If the fuel flow isn't a steady full flow, Check the pump and then check the filter head. You may have to check back to the tank outlet. Operating the bucket as you have is not much load, and you dropped 1200 rpm so it's probable that you have a serious fuel flow restriction.

 

[GodHungry777]

Did you check the actual fuel flow to the injector pump? Since you had "...water and gunk..." in the tank, you might have crud in the head of the fuel filter that is restricting flow. If you have a lift pump, is it functioning properly?

I would disconnect the line at the line going to the Injector pump and crank the engine and look at the fuel stream coming out of that fuel line. ( if you have an electric fuel pump, turning on the key should activate it.) It should be a full stream, not intermittent or dribbling. If the fuel flow isn't a steady full flow, Check the pump and then check the filter head. You may have to check back to the tank outlet. Operating the bucket as you have is not much load, and you dropped 1200 rpm so it's probable that you have a serious fuel flow restriction.

How's the flow here?

 

[JerryMT]

How's the flow here?

 

[GreensvilleJay]

Fuel pump looks and sounds OK to me.....very similar to my BX23S.
Does the engine run fine at say 2500(or 3000 ) RPM for 20-30 minutes continuous runtime, without 'bogging down' or 'losing' power ?
Does it ONLY lose power when you apply 'hydraulics' ? IS it ONE specific lever/valve operation or will ANY/ALL levers/valves cause it to lose power ?
If so... either something in the hydraulics is the problem or perhaps weak low) compression.

This 'remote diagnosis' is difficult but by process of elimination, we should be able to figure this out...

 

[JerryMT]

I'm not familiar with this specific machine but I assume the fuel output you are showing is from the connection to the injector pump (IP) connection. If so that looks like adequate fuel supply between the tank, the main filter, the lift pump, auxiliary filter, and to the IP.

If the problem is not restricted fuel supply, then it must be load related. Does it occur on each of the control functions or just the bucket curl function? You say you changed the hydraulic filters and replaced the fluid. I presume you changed the return filters. It's possible that you have whatever was on your filters and in the sump clogging part of the hydraulic control system and either a return passage is clogged or relief valve isn't opening.

Can you measure hydraulic system pressure? Look for a "T" in the pump(s) high pressure lines where you might put a 5000 psi liquid filled gauge (you'll need that high of a pressure gauge because of pressure spike as the cylinder stop, etc.) If there is no test "T" than you can put one in. Then you can actuate the various control functions and see when the high load (high pressure) occurs and is held on after releasing the control lever.

 

[North Idaho Wolfman]

Your fuel looks.... off?
Is it old?
Is it biofuel?
Does it have petrol in it?

Here, off road diesel is RED, over the road is clear with a tint of Blue / Green, contaminated fuel is yellow.

Ok now another possibility, that's a high flow, high pressure pump and feeding too much pressure or flow to these injection pumps on these engines can cause issues, check and make sure the return on the injection pump and on the injectors is free flowing.

 

[woodman55]

Check your blow by, that's always a easy check to see if the rings are done.

 

[GodHungry777]

Fuel pump looks and sounds OK to me.....very similar to my BX23S.
Does the engine run fine at say 2500(or 3000 ) RPM for 20-30 minutes continuous runtime, without 'bogging down' or 'losing' power ?
Does it ONLY lose power when you apply 'hydraulics' ? IS it ONE specific lever/valve operation or will ANY/ALL levers/valves cause it to lose power ?
If so... either something in the hydraulics is the problem or perhaps weak low) compression.

This 'remote diagnosis' is difficult but by process of elimination, we should be able to figure this out...

2500RPM (recommended Max for KX41) it still looses RPM under load - drops to 1200RPM.
Looses power on all hydraulic actions but not equally on all actions. Higher load actions reduce RPM more dramatically. Eg. lifting arm drops more than lowering arm, pushing bucket drops more than pulling bucket, etc.

 

[GodHungry777]

Your fuel looks.... off?
Is it old?
Is it biofuel?
Does it have petrol in it?

Here, off road diesel is RED, over the road is clear with a tint of Blue / Green, contaminated fuel is yellow.

Ok now another possibility, that's a high flow, high pressure pump and feeding too much pressure or flow to these injection pumps on these engines can cause issues, check and make sure the return on the injection pump and on the injectors is free flowing.

Fuel is premium diesel. Probably just a difference in colour between US and Australian standards.
Pre-IP return to the tank is definitely free flowing. It pours in there pre-startup.

 

[GodHungry777]

I'm not familiar with this specific machine but I assume the fuel output you are showing is from the connection to the injector pump (IP) connection. If so that looks like adequate fuel supply between the tank, the main filter, the lift pump, auxiliary filter, and to the IP.

If the problem is not restricted fuel supply, then it must be load related. Does it occur on each of the control functions or just the bucket curl function? You say you changed the hydraulic filters and replaced the fluid. I presume you changed the return filters. It's possible that you have whatever was on your filters and in the sump clogging part of the hydraulic control system and either a return passage is clogged or relief valve isn't opening.

Can you measure hydraulic system pressure? Look for a "T" in the pump(s) high pressure lines where you might put a 5000 psi liquid filled gauge (you'll need that high of a pressure gauge because of pressure spike as the cylinder stop, etc.) If there is no test "T" than you can put one in. Then you can actuate the various control functions and see when the high load (high pressure) occurs and is held on after releasing the control lever.

Yes it occurs on all hydraulic functions but to varying degrees depending on the load - eg. raising arm drops RPM more than lowering arm, pushing the bucket drops RPM more than pulling the bucket.

Suction and return filters were both changed. Both were terribly clogged. Return was so clogged that it had pulled apart from the pressure. But replacing them hasn't made any difference.

I'm still trying to get hold of a pressure gauge.

Can anyone confirm that the steel block standing up at the end of the control block, which is connected to the return channel to the tank, is the relief/check valve? (see image). looks like the one in the manual.

 

[Trustable]

I was going to say you need to check the pressure relief valve.
But I'm also not liking the way the engine sounds, it does not sound like it's firing properly.

Nothing really externally on low compression.
I would also suggest that you do that before you invest more time and money in it.
Compression testers are cheap.

Most of the smaller chain auto parts stores will even let you rent one for no cost in my experience. Edit: just saw he is in Australia so that may not apply.