Help with Kubota KX040 mini-excavator getting air in the fuel.

[Sodo]

Had to do this to get to the fuel pump.

To observe the fuel on it's last leg from the filter into the injector pump I added a section of clear hose.
All that air is going into the injector pump.
It runs, but stumbles when you try to do some work (I suppose when it opens the throttle)
I bought the shop manual, and as usual, I should have bought it last week.

Here's the fuel system (from the repair manual).
The water separator is on the suction side of the fuel pump and I'm "pretty sure" it doesn't leak.
I removed the fuel tank and cleaned it out super clean.
There was nothing in it but a tiny bit of water and sediment, real clean.
Now its so clean you could eat out of it.

So what I need help with now is, how can I find where the air is getting into the fuel system?
It must be on the suction side.

It doesn't drip any fuel when shut down.

Do I pressurize the suction-side and spray soap on the hoses?

Are there any tricks to find an air leak on the suction side of the fuel system?

 

[Sodo]

========

IDEA: Air entering the system MUST be between the pump and the tank
On the suction side of the pump.

Maybe pinching off the hoses at R & T can narrow down the source of the leak?
I will try that tomorrow.

 

[34Willys]

On the diagram, you need to show where you 'opened/disconnected' the system. Did you replace the fuel filter, etc.
Had a Ford F-350 6.0 TD in my shop a while back, and replaced the fuel filters. Spent a day and a half trying to bleed the system of air bubbles. Turned
out the aftermarket filter was .003" smaller than the original and would not completely seal the filter housing causing the pump to low
pressure cavitate and induce air bubbles into the fuel stream.
Looks like you have a similar issue.
Patrick

 

[Agvg]

Would just replace all hoses with new quality ones, any strain in the tank? Any suction pipe in the tank? Have seen cracks in such pipes, the same behaviour with full tank?

 

[mini14]

Had a hino fuel filter gasket that started pulling air after a few thousand miles. Poor gasket design. The aftermarket filter design is better than oem..

 

[Sodo]

It must be a leak in a hose, but wouldn't it drip diesel when parked?
No leaks anywhere.

The owner took it to the Kubota dealer yesterday.
I was 'fixing' in exchange for digging.
But it wasnt digging well, and I wasnt fixing well so we had to go to plan B.
The tech there said the air is not right, but the machine can eject some air.
Said there are other things that need to be verified, such as the "regen" system so it could be a combination of problems.

Thanks for the ideas, every bit helps!

 

[Agvg]

Og might suck air without leaking fuel, so replacing old hoses are a always a good idea but get good quality hoses, a lot of junk fuel hoses on the market.

 

[Industrial Toys]

I have just about lost my mind with a kubota powered generator sucking air. Everything I systematically look at seems fine. It's messing with me big time! Same thing. Sitting, the fuel line should siphone fuel out of the tank and leak, but it doesn't. I am guessing that it only takes the slightest leak to allow air into the system at rest. BUT, I suspect I have more than one little problem, as is often the case with troubleshooting. My machine had all new hose with Parker push-on ends , hydraulic connectors, RACOR Filter. Sounds good, but but had no history of ever working with THAT fuel system, so now find the problem. Sometimes you even replace good stuff with bad while trying to find a problem.

Good Luck.

BTW, where do they store the full size spare tire on those?

PS. I also tried prssurizing the system and no leak. I suspect, that a system can suck air while in suction, that won't leak when you put it under pressure.

IF I had known the dozens and dozens of hours I had wasted on this, I would have rigged up a suction testing rig, without question. Although that is not easy to employ either, trying to find the leak.

 

[R44]

Well what was the problem
having the same issue with mine