Kubota KX41 revs dropping when hydraulics are activated

GodHungry777

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
Ok, that's what I was going to ask was if it looks like some has gotten in there.
So that's a no, and your right no it's not going to jump time on it's own.

I've lost my place on this issue, so from the top:
Have you done a compression test?
This will tell a lot.

Have you had the injection pump and injectors professionally tested?
Because just because it put out fuel, it does not mean it's putting it out at the right psi.

I would safely say you have eliminated the hydraulics as any part of the issue as disconnecting it didn't make the engine run normally.

The slow rise in RPM and the drop in RPM when loaded are pointing to either the injection pump or the Governor.
Let me dig into the governor specs and adjustments and see if anything pops out, but I'm really leaning to the issue being in the injection pump or injectors.

Have we bottle feed the injection pump just to rule out any diesel supply flow possibilities?
Yeah the IP is where I think I need to go deeper. The injectors have been professionally tested but not the IP.
The IP has shown:
  • that it does pump fuel
  • That the fuel slider moves freely
  • that it sends good spray through the injectors
So yes, I'll go deeper on this and see if I can get it checked by a local diesel shop.
 

North Idaho Wolfman

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Also do a compression test!
It might be fooling you and have a dead cylinder.
That would really explain it falling off.
 

JerryMT

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Kubota M4500, NH TD95D,Ford 4610
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Yeah the IP is where I think I need to go deeper. The injectors have been professionally tested but not the IP.
The IP has shown:
  • that it does pump fuel
  • That the fuel slider moves freely
  • that it sends good spray through the injectors
So yes, I'll go deeper on this and see if I can get it checked by a local diesel shop.

  • "checked governor spring, forks and flyweight. Worn but nothing broken or missing"
From your first post, "worn" is the operative word. Could that be the problem?

And you still have the hydraulics to figure out.
 

GodHungry777

Member

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Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
Also do a compression test!
It might be fooling you and have a dead cylinder.
That would really explain it falling off.
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?
 

North Idaho Wolfman

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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?
Yea you've got one lagging cylinder, but I've seen far worse!
You should be fine there.

Sorry if this is a repeat, but have you have the injectors pop tested and pattern tested?
Have we bottle feed the injection pump so no other variables in fuel supply are playing a role in this?
 

GodHungry777

Member

Equipment
Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
Yea you've got one lagging cylinder, but I've seen far worse!
You should be fine there.

Sorry if this is a repeat, but have you have the injectors pop tested and pattern tested?
Have we bottle feed the injection pump so no other variables in fuel supply are playing a role in this?
Yes the injectors have been professionally pop and pattern tested. All clear.
Depends what you want to eliminate from the system with the bottle feed.
I've bypassed the filters - no change.
I haven't tried running it without the lift pump. Will gravity feed without lift pump supply enough fuel?

I think the governor is the only remaining fuel system component we haven't changed.

On adjustments, there's are a few that I'd like to figure out how to make sure they are at the original factory setting.
1. The one on the bottom side of the Injector Pump
2. The one on the front side of the Injector Pump
3. The number of shims that should be present under the Injector Pump (timing)

Regarding the shims, the KX41H exploded parts view shows three shims (0.2mm, 0.25mm and 0.3mm). How do I know what shims should be there? Mine has two shims. i haven't looked to see what sizes they are.
I assume that the parts view shows three shims because there are three possible sizes you can order? Not because you need all three on your machine?
 

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North Idaho Wolfman

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L3450DT-GST, Woods FEL, B7100 HSD, FEL, 60" SB, 743 Bobcat with V2203, and more
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Sandpoint, ID
Yes the injectors have been professionally pop and pattern tested. All clear.
Depends what you want to eliminate from the system with the bottle feed.
I've bypassed the filters - no change.
I haven't tried running it without the lift pump. Will gravity feed without lift pump supply enough fuel?

I think the governor is the only remaining fuel system component we haven't changed.

On adjustments, there's are a few that I'd like to figure out how to make sure they are at the original factory setting.
1. The one on the bottom side of the Injector Pump
2. The one on the front side of the Injector Pump
3. The number of shims that should be present under the Injector Pump (timing)

Regarding the shims, the KX41H exploded parts view shows three shims (0.2mm, 0.25mm and 0.3mm). How do I know what shims should be there? Mine has two shims. i haven't looked to see what sizes they are.
I assume that the parts view shows three shims because there are three possible sizes you can order? Not because you need all three on your machine?
You wouldn't gravity feed the lift pump you would gravity feed the injection pump directly, eliminating anything else!
I would try that.
I'll have to look into the 2 adjustments and see if any of the rebuild books show how to set those, they are normally just limits for RPM.

The shim count is done with a spill test, it should be in the WSM.
Doing that would be a good idea.
And yes the parts view is just representative, actual shim count varies and there is no set amount.
 

GodHungry777

Member

Equipment
Kubota KX41 with D1105 engine
Dec 23, 2022
35
5
8
Australia
FINAL UPDATE - PROBLEM SOLVED
Ok. So after replacing the entire fuel system, the problem was where we first started - the governor flyweight sticking.
NB. For future reference, see my earlier video of the engine running with the throttle plate off so the governor fingers are visible.
My original questions in pursuing the governor were to see if anyone knew if the movement of the governor fingers should be noticeable. I wasn't sure if the governor adjusting the throttle slide would be big enough to see it move if it was just making very minor adjustments to the slide.
I would now suggest that if you don't see the fingers move under changing load conditions, you should head to the governor flyweight first.
Here's the difference between the old worn/faulty governor flyweight and the new one.
I have no regrets in replacing and repairing the entire fuel system along the way. Everything that was repaired or replaced was in terrible condition and I couldn't believe it was running at all in the condition they were in.
Thank you to all for your input along the way. It's been a great education.
Let me know if you have any questions about the process.
 
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