Need help with Kubota KX040 FUEL PROBLEM

   / Need help with Kubota KX040 FUEL PROBLEM #11  
the air would come from before the lift pump, run a hose to the lift pump and a jerry can,
   / Need help with Kubota KX040 FUEL PROBLEM
  • Thread Starter
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”.
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   / Need help with Kubota KX040 FUEL PROBLEM
  • Thread Starter
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.
   / Need help with Kubota KX040 FUEL PROBLEM #14  
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
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   / Need help with Kubota KX040 FUEL PROBLEM
  • Thread Starter
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.
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   / Need help with Kubota KX040 FUEL PROBLEM #16  
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
   / Need help with Kubota KX040 FUEL PROBLEM #17  
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.
   / Need help with Kubota KX040 FUEL PROBLEM
  • Thread Starter
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.
   / Need help with Kubota KX040 FUEL PROBLEM #19  
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.
   / Need help with Kubota KX040 FUEL PROBLEM
  • Thread Starter
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.