L4240 losing power blowing smoke and surging

[Lightning93]

The first time this happened was a couple months ago while brush hogging it was down to about a 1/4 tank of fuel then started to act up,I limped it back to the garage and changed the fuel filter thinking that would have been the problem an toped it off with fresh fuel.
Filter looked pretty clean and didn't notice any water in the fuel I ued the machine a few times since it seemed fine until last night while moving snow again down to about a 1/4 tank and it started doing the same thing again.
Could this be bad fuel?? If so why would it run ok full if there was water in the fuel shouldn't it be in the bottom of the tank

 

[Tooljunkie]

Pickup in tank partially blocked ?

 

[85Hokie]

I agree with TJ, something catching in the pick up - also - just for the hell of it, check you air filter too.

 

[rbargeron]

My L48 was doing something like that last summer - when the fuel gauge got below 1/4 it would run rough and topping it up cleared it. I found the plastic fuel tank collapsed like a deflated beach ball - loosening the fuel cap gave a whoosh as air rushed in. The fuel cap's vent was plugged with dirt so the transfer pump pulled a vacuum on the tank. The deformed tank made the gauge read wrong and affected the pickup level too. Running with the cap loose the tank partly regained its shape. The cap's been replaced but not the hard-to-remove tank. Keeping it above 1/4 avoids trouble. Some hot day next summer when the machine is hot from work I might try expanding the tank with air. (hold my beer and watch this!!)

 

[aeblank]

Seal it up tight on a cold morning, and put it out in the sun to warm......

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[RCW]

I'm with Tooljunkie and Hokie.

But another thing - its at 1/4 tank each time.....Kubota fuel gauges are notoriously inaccurate.... Wonder if its starving for fuel.

Keep it full of fuel all the time. Better for avoiding collecting water, condensation, etc.

Gets to half-full - - Fill it! Doesn't sound like you're doing 8 hours/day with it, so its a good practice.

As soon as my little BX gets off the FULL line, it will take 3 gallons, easy, which is half a tank.

Good luck!

 

[Bulldog]

What color is the smoke and how bad is it?

 

[Dave_eng]

I cannot speak specifically on your model of tractor but most are designed in the way I will describe if the fuel tank filler is above the engine.
When the fuel tank is half full or more and you are operating on level ground, gravity will deliver fuel from the tank to the injection pump.
If tank levels are lower and further, if you are on sloped ground, the gravity fuel feed no longer works and designers incorporate lift pumps to move fuel from the tank to the injection pump.
The lift pump is usually some sort of simple mechanical pump mounted on the side of the engine. If you follow the fuel line from the bottom of the tank you will come to the lift pump which is usually before the filter but not always.
Sometimes, the lift pump will be electrical. It will look like a metallic cylinder with two fuel connections and some wires coming out of it.
When you start running out of fuel with the gauge still showing fuel in the tank, suspect the lift pump is not delivering fuel to the injection pump.

Dave M7040

 

[Lightning93]

Ok so this is what I've found so far in the short time I had to work on it today,fuel gauge read 1/4 tank I disconnected the fuel line from the tank to the filter Assembly to 1 check for a good flow of fuel and 2 to see if the fuel looked to be contaminated ,so put a nice clean catch can under it. fuel flowed with no problem from the tank and looked absolutely clean no visual signs of contamination and I got approximately 2-1/2 gallons into the catch can before the tank was empty,su the guage must be if not exactly correct,pretty darn close.
Removed the sediment bowl to get a better look at the filter and that looked perfectly clean as well but I put s new filter back in,I had one so why not.
I put roughly 2-1/2 gallons of fresh fuel back in the tank to see if I could replicate the issue.
Followed the steps for bleeding the air according to Kubota opening the fuel petcock filling the sediment bowl,and opening the air bleed valve.
Started the tractor it started and ran for about 10-15 seconds then stumbled and stalled.
I attempted to start it a few more times being carefully not to overheat the starter.
At first while attempting to start I would get black smoke coming from the exhaust and it would try to start but just wouldn't get running.
Now after a few attempts under cranking not much smoke at all,so now I'm thinking either there's air in the injector lines,or I'm hoping the small mechanical lift pump is just not doing its job?

Here's what I'm thinking does this make sense?
It's seems to be happinng when it gets somewhere around a 1/4 tank of fuel so now that I now the guage is accurate I'm wondering if when it gets that low if there is not enough pressure from the tank not being full to supply the lift pump.
Does that make any sense?
I'm thinking tomorrow I'll take the line off the filter housing to the lift pump,see if I have fuel there,then I guess take the line off the lift pump going to the injector pump and crank it and see what happens.
Hopefully I'm heading in the right direction?
Thanks a lot for all the responses.

 

[Lightning93]

I cannot speak specifically on your model of tractor but most are designed in the way I will describe if the fuel tank filler is above the engine.
When the fuel tank is half full or more and you are operating on level ground, gravity will deliver fuel from the tank to the injection pump.
If tank levels are lower and further, if you are on sloped ground, the gravity fuel feed no longer works and designers incorporate lift pumps to move fuel from the tank to the injection pump.
The lift pump is usually some sort of simple mechanical pump mounted on the side of the engine. If you follow the fuel line from the bottom of the tank you will come to the lift pump which is usually before the filter but not always.
Sometimes, the lift pump will be electrical. It will look like a metallic cylinder with two fuel connections and some wires coming out of it.
When you start running out of fuel with the gauge still showing fuel in the tank, suspect the lift pump is not delivering fuel to the injection pump.

Dave M7040

Thanks Dave helpful information, I am getting fuel out of the lift pump,question is how much of a flow should be coming out of the lift pump?


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[Dave_eng]

Lightning
Tell me how you know the lift pump is working.
If you have more than 1/4, tank, gravity will move the fuel through the lift pump even if it is broken.
Is there a hand lever on the bottom of the pump so that you can manually bleed the system up to the injector pump?
The lift pump can suck fuel up hill so it is not relying on the level of fuel in the tank to get its fuel. Kubota would never design a tractor which could not use almost the last drop of fuel in the tank!
Bleeding the injector lines one by one seems to be required. Are your glow plugs working properly?
Sometimes when mechanical lift pumps fail i.e. when there is a split in the diaphragm, diesel will go into the crankcase. You need to check that you dont have several litres in with your oil as it is not a great lubricant. Sometimes you can smell it in the oil and usually the oil level is above the dipstick mark.
Waiting for your reply!!!!.
Dave M7040

 

[Lightning93]

Lightning
Tell me how you know the lift pump is working.
If you have more than 1/4, tank, gravity will move the fuel through the lift pump even if it is broken.
Is there a hand lever on the bottom of the pump so that you can manually bleed the system up to the injector pump?
The lift pump can suck fuel up hill so it is not relying on the level of fuel in the tank to get its fuel. Kubota would never design a tractor which could not use almost the last drop of fuel in the tank!
Bleeding the injector lines one by one seems to be required. Are your glow plugs working properly?
Sometimes when mechanical lift pumps fail i.e. when there is a split in the diaphragm, diesel will go into the crankcase. You need to check that you dont have several litres in with your oil as it is not a great lubricant. Sometimes you can smell it in the oil and usually the oil level is above the dipstick mark.
Waiting for your reply!!!!.
Dave M7040

This is what I have done,starting at the inlet to the filter housing I took off the line there plenty if flow from the tank then to the outlet of the filter housing I have flow there to the inlet of the lift pump however on the out of the lift pump going to the injector pump it will not flow just by gravity.
It's only under cranking that I get anything out of the injector pump side of the lift pump there is no lever on the lift pump itself.
I do believe I will have to bleed through the injector lines,I'm just curious if I need a new lift pump first.
Thanks for the replies I appreciate it very much

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[D2Cat]

Why not just fill the tank with fuel. Bleed the system. Use machine and see what happens. If it does the same when down to 1/4 tank, replace lift pump.

 

[Lightning93]

Why not just fill the tank with fuel. Bleed the system. Use machine and see what happens. If it does the same when down to 1/4 tank, replace lift pump.

On the L 40 series its a real pain in the ass to get to the injectors to bleed them.
And the fact that if the lift pump is no good its putting more stress on the injector pump itself.
But that maybe what I do, more snow coming .



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[Dave_eng]

Lightning
Do you have an operators manual with bleeding instructions?
Usually there is no need to crank engine to move fuel as far as the injection pump because some manual method is available.
Since you know your machine will run with a full tank, why not just operate it that way until warmer weather?
Dave M7040