Need help with Kubota KX040 FUEL PROBLEM

[Sodo]

It won't run at full-power.
It stumbles and dies periodically (often).
I am able to work it lightly at about 1/3 throttle, but whenever the control system pours the coal to it, it stumbles and often quits.
When not stumbling, the engine is perfectly smooth.
I'm not a diesel mechanic but I may be on the path to becoming one (just for this machine).
Fuel filter looks recent. Poured it out into a pan and no sediment appeared.
Air filter is recent (looks new too).
This problem is on-going for years, Kubota dealer unable to fix it.
Kubota dealer replaced the injectors at about 400 hours which did not eliminate the problem, which has become much more frequent.
I think possibly they have a harder time identifying the problem because the Kubota dealer can't dig with it.

2016 KX040-4, 1400 hrs, 9800 lbs

Not my machine. Owner is letting me borrow it to dig at my place in hopes I might find the problem and he knows I'm a persistent sob.
He needs to lend it to a genuine diesel mechanic, but that opportunity has not arisen.
But I'm happy to have it here even if I have to run it at 1/3 throttle.

=========

There's an air bleeder valve at the top of the fuel filter block.
Opening it often ejects some air.
I put a clear hose onto it and eject into a fuel can, and eject air, until it's fully clear of air.
But later the problem returns and I check the ejector valve and there's air bubbles in the fuel stream.
It acts (to me) like there's a candy wrapper in the tank that periodically gets sucked onto the inlet. Then it stumbles, the machine lurches, and the wrapper washes away, clearing the inlet.

What I've done:
Clean water separator. It shows no air bubbles in the visible part. It has a new o-ring.
Removed and cleaned the fuel tank. Removed the fuel level sensor, so I could LOOK inside the tank. There was only a very tiny amount of sediment/water in the bottom. I made it so clean you could drink out of it. Tank is frickin' clean.

I blew out the line from the water separator to the tank with compressed air.
There is a vent line to the tank that has a one-way valve. I sucked on it and it flows one way (to the tank) cannot blow out to it.

On the fuel separator (which is under suction from the fuel lift pump) one of the nipples is 'ever so slightly' loose. I can wiggle it. It seems like it can let in air, but can't be much. This nipple fitting is like a glued-in/crimped in fitting, a permanent nipple on the separator.

One question I have, is, does a modern Kubota have an air ejection process capable to eject air? The air I'm ejecting from the fuel filter (manually) ..... can the system do this on it's own?

 

[RickB]

You found the problem, the loose nipple on the water separator outlet. If there are no visible bubbles in the clear part of the separator the problem has to be between it and the fuel filter where the air is found. Exactly where the loose nipple is. Diesels will not tolerate the steady introduction of air into the fuel supply.

 

[Sodo]

thanks for your attention RickB!

Here's the system from the Messick's site.
Dang it doesn't have the injector pump, I'll go get that pic.

I took the separator off. The wiggly outlet holds vacuum, it cannot be the leak. There must be an O-ring in there. Nevertheless I eliminated the whole water separator with the copper tube -- and I'll go dig again but I'm not optimistic.....

OK so you are saying the system cannot have ANY bubbles in it, that the system does not automatically eject air?

Here's my idea: Put a long clear hose between the filter and the injector pump and route the hose past the operator seat.
Where I can watch for bubbles passing by to the injector pump.

 

[RickB]

Diesels will not tolerate the steady introduction of air into the fuel supply.

That is what I said.
You might think there is an o-ring sealing that nipple. I think there is not. One of us is mistaken. Your test results will be interesting.

 

[Sodo]

Dunno. It holds vacuum. Maybe it takes little sips of air under vibration.
But it's outta there, replaced by a copper tube for now.

I was moving forward on my project to watch (while operating) for bubbles going by (thru a clear tube) to the injection pump.
I started the lift pump to pre-fill the tube and noticed the flow is almost nothing out of the filter. So thats a big clue of course when a machine could be starving for fuel.
:thumbsup: Clues are good. :thumbsup:
Filter looks "new", so we didn't suspect it, but could be plugged with algae or something?

I ran the lift pump for awhile (ahead of the filter) and it was pretty slow but then started belching out air and the flow increased. The air depleted and it doesn't seep like any more air is entering the system. So the pump was cavitating, not building flow or pressure.

I took the filter block off and inspected it carefully. No apparent problems.
But where do I get another filter on a Sunday....??

I'll try putting it back on and see if the flow out of the filter increases.

OK theres some Sunday reading for ya. Hope you all are having a good weekend!

 

[Sodo]

I bypassed the filter block.
I sealed the wiggling nipple on the water separator.
No change. It still burps air out of the bleeder.

So I proceeded ahead with my plan to add a clear line to observe the fuel that goes directly into the injector pump.

That hose is the last hose, directly to the injector pump
All that air is going into the injector pump.
It seems to run OK, I tracked it up a steep hill but I didn't push a pile of dirt with the dozer blade.
I'm gonna dig with it tomorrow and see if it can put out work with that much air in the fuel.
But even so, this CANT be right.
There is no reason Kubota would allow so much air into the fuel, there HAS to be a leak somewhere.

The fuel system is complicated, there's a fuel cooler, and couple check valves, and maybe the worst thing is, you have to remove the counterweight ( 1069 lbs! ) to get to the (fuel) lift pump.

So I bought the danged shop manual.
And as usual, I should have bought it last week.

This just keeps getting deeper and deeper.
But just the 4-hour roundtrip to the Kubota dealer (2 times), and the machine owner's lack of faith that they can fix it when they failed before, he wants me to keep trying.
What I will get out of this is he'll likely lend gthe machine to me anytime, so this is good.:thumbsup:

So what I need help with now is, how can I find a suction air leak in the fuel system?
If I could pressurize it and spray soap on the hoses,
but if it's only a suction leak not a pressure leak that may not reveal it, but it may.

Are there any other tricks?

 

[Sodo]

The owner took it to the Kubota dealer.
Kubota tech said there are lots of other things it could be in addition to air, such as the regen acting up.
Which I never even considered.

 

[JerryK]

On the 24 valve Dodge Cummins diesels, they went with a electric lift pump mounted on the left side of the motor. [ no cam lobe to run a mechanical ] The VP44 injection pump required positive fuel pressure, and this lift pump pulled fuel from the frame mounted tank. Some of the trucks developed leaks in the flex line going from the frame mounted steel fuel line, up to the motor. It would suck in very small amounts of air which a lot of folks pulled their hair out finding. Mounting the lift pump onto the frame, along with replacing the line going to the motor, generally cured the problem [ all though the lift pump itself was a pain in the arse ] So any flexible line could be suspect. So any line/device in the area where the fuel is being ' sucked ' is where I would look. [ good luck and stay safe ... !!!!!!!!!!!!! ]

 

[nateatvtc]

Did the owner ever get to the bottom of this? We're having identical issues with a kx040

 

[Sodo]

I ran the fuel out of the water separator, thru a long clear vinyl hose past the operator seat so I could see the bubbles going into the injector pump. I conclude that the Kubota injector pump can tolerate or eject some air. I don’t know how much - but it tolerates much more than I expected. Long strings of bubbles.

I found several possible leaks on the suction side. Fixing them didn’t solve the problem.
1) water separator had no o-ring. I was certain this was the culprit. Nope!
2) Elbow fittings at the water separator “wiggled”. I pulled them out, sealed very carefully with Permatex gray and put them back in. Tested with vacuum and it was tight. Still there was air entering the system somewhere.
3) Fuel “wetness” at the lift pump suction hose nipple. This is very difficult to access behind the counterweight. I fussed with it as best I could, moving the clamp to a “more proper” location on the nipple bead. And still it had bubbles passing by (in the clear hose) to the injection pump.

Dealer#2 told the owner that the machine had the “wrong fuel filter”, that the 040 has a “specific required fuel filter dependent upon the _machine serial number_” and said the whole problem was this. And said not to let non-qualified people mess with his eqpt. Well Dealer#1, 4 hours away who put the wrong filter on, and replaced the injectors, holding the machine for weeks, might be non-qualified too I say.

OK good luck! Simplest thing to try is the serial# specific fuel filter. And please let me know if this solves it. I’m curious if Dealer#2 was blowing a little smoke, perhaps not at me but at Dealer#1 (a notorious Kubota sales-price undercutter 4 hours away that other dealers hate on). My impression of Dealer#2 was the tech was very good. I think they like to promote their services, but even so, he was the real thing.

 

[laurencen]

the air would come from before the lift pump, run a hose to the lift pump and a jerry can,

 

[Sodo]

Tried that….

In this pic you can see that I tried a Jerry can. I was in the middle of this when the owner got the call that a master tech was willing to work on it - so he quickly collected his machine (while I was mid-test in the Jerry can stage). So I never got to follow that to the end.

This problem totally blew me away. The fuel system schematic was more complicated than that and I didn’t fully understand it.

By this time I was suspecting the Regen system or computer update, or who knows what?

Dealer#2 said it was due to an improper fuel filter ( by machine serial # ). I don’t know if that’s the “full story”.

 

[Sodo]

Did the owner ever get to the bottom of this? We're having identical issues with a kx040

I talked to the owner, he is still having trouble with his 040 over the past year. He said he has been changing the fuel filter often, sometimes after only 2 weeks which seems to always 'work' for the short period. And he knows he's not putting dirty fuel in the machine, in fact being super careful because of this. And last time I took the tank out, to inspect for some junk inside. There was nothing in the tank, only a tiny bit of sediment.

This suggests to me that the machine has some borderline fuel supply problem that a clean free-flowing filter solves only for a short time. He's going to bring it back to me for a little while again soon. He needs this machine for his construction business, but I like to dig a little at my house from time to time, so we work it out. I will put a clear vinyl fuel line that I can see from the operator seat and dig with it.

I will check some other things too, verify lift pump output flow, and if the injection pump is pulling a vacuum on the lift pump.

If you have discovered anything please LMK.
If you have info it would be great to organize a chat on the phone.

 

[laurencen]

years ago had a Cat 420d, still do but when I first received it would only run high RPM on initial start, would run all day at 50%, had the dealer work on it couple times best they came up with was a switch to activate the lift pump, after a few years started digging into it and found a relay on the frame under the cab noted as lift pump relay, it was dropping out when the motor started, besides was a fuel shut off relay and this was activated by the key, when turned to start the relay would close, pump relay was activated and it started, problem was once the motor runs you let go of the key, at this point the pump relay should be latched to keep pump running but it was dropping out

changed the relays and ran 100% since that time, when the pump runs no air is getting into the lines but when the pump drops the injection pump is sucking and had lots of air, at lower RPM the air significantly reduced and it ran fine

may be a similar issue to yours

 

[Sodo]

Excellent Laurence! Thank you. I will find a way to verify voltage (& current supply) to the lift pump!!
I hear the pump when you switch the key on but it could be interrupted and then the injection pump may be drawing suction during interruptions.

 

[laurencen]

exactly, the pump needs to run all the time on the Cat, it is held in with the relay, in my case it dropped when the key was moved from start to run, worth checking

 

[Seven Gables]

Just wondering if you ever did that flow test on the lift pump? Think at this point for the relatively small cost I would replace the fuel supply hose and clamps from tank to water separator and also from water separator to lift pump. If there's room for two hose clamps on your hose barbs I'd put two on. I just finished replacing the entire fuel supply system on my sterling sc8000 from tank which is mounted low behind rear axle to the inj pump. This 2002 truck has the 5.9 Cummins with the infamous vp44 Bosch inj pump. Good luck with your s.

 

[Sodo]

I got to run the machine again and it still has a similar problem, but ONLY when it's cold (dies often).
It's not as bad as before, but the machine has 300 more hours since I worked on it last.
All we know is the dealer/tech replaced the fuel filter with a unit specified by Kubota for that specific machine serial#.
Which seemed to fix the problem.

Dealer/tech said "don't let unqualified people work in the machine".
Which is certainly wise at many levels.
But when all the operators are working on it with vise-grips.... and the dealer is booked out 6 weeks.... I might be his best bet.

If I get time to work on it again I'll check the 12v electrical supply to the lift pump _while in operation_. The 12v supply to the lift pump could be "intermittent".....where the engine fuel pump sucks air into the supply line during those moments when the lift pump goes dark.

This is a wild guess but not difficult to test.

 

[Jmtearthworks]

Hi, my kx040 has the exact same issue. Has been going on for years, the dealer has looked over it several times but hasn't been able to find the problem. Is there a way to fix this or do I just have to live with the machine stalling and losing power over and over.

 

[Sodo]

Have you read the whole post? Tried anything? I never solved it then the owner took the machine back. I think it's still happening sometimes, but the machine is "usable" at a little lower power levels.
My plan next, that I didn't get to do....
1) Bypass the lines after the lift pump ---- supplying the injection pump with a replacement loop, see if the injection pump was sucking air in from that segment. The lift pump is not easy to access.
2) Hang a tank from above, try supplying the injector pump by gravity thru a short hose.
3) Add a small lightbulb to the (electric) lift pump on a long wire that I can see from the cab, to monitor if lift pump power supply is consistent.