Ran Great Until It Didn't

[Farmer Brown]

I am having issues with a Kubota KX121-3 S Series Mini-Ex. (2200 hours) the machine was parked for 3 weeks and not started but was running great when last shut down. The next time it was started it started perfect and idled fine while it was warming up. The as I started to drive \it started bogging down and sounded like the engine was about o die. I let off the forward controls and the engine smoothed back out and seemed okay. I checked the fuel gauge and it was at 3/4 tank. I was starting down a hill so thought it may have been about out of fuel which is what it sounded like. I managed to baby it down off the hill to a lower area to do some work and it seemed to get better as the machine continued to warm up. However when I when to use the bucket it would almost die again. It did this three or four more times and then it cleared up and ran perfect the rest of the time I used it that day Approximately 4 to 5 hours work time. The next day I went to use it again and this time it would not clear up and run no matter how long I let it warm up. I finally shut it down.

A couple days of sitting once again due to rain I purchased a new OEM fuel filter from Kubota. Also purchased diesel fuel additive that was supposed to remove any water, slime or algae from tank and also was supposed to clean injectors etc. ($20 + per bottle.) I added the prescribed amount of additive to the fuel tank. I then removed the sediment bowl and cleaned it out. There was no water in the bowl at all, but had a tiny amount of what looked like dirt possibly in bottom of it. I then removed the air filter and inspected the (outer air filter) It had some dust in it that I was able to tap the filter and it seemed to knock it out and I stopped when no more dust fell out then replaced it and reassembled the filter canister.

I then tried to start the machine and the sputtering and bogging down started immediately. I decided to let it run for a longer period of time to let the fuel additive and cleaner have time to work through the fuel system but it never cleared up. The machine with no load and at idle or with the throttle up to mid- way it makes no difference. It will run perfect then suddenly start to miss and then almost die and shake and sputter, puffs of black/white smoke then clear up run perfect then after few seconds or at times maybe even 2-3 minutes it will again go through the sputter event again. Doing this over and over no matter if engine has warmed or not. What else can I possibly check and also if it's an injector pump is there a way for me to check this to be sure without special tools etc. before purchasing one. Any help is appreciated as I get further behind by the day. Thanks in advance!

 

[Tags]

Could be the fuel pump, you should be able to hear it if you turn the key to the run position and walk around to the engine compartment, you should hear a "ticking" sound, that's the pump pumping. Did you do this after changing the filter to bleed the fuel system. You're supposed to do it for at least a minute and it will self prime the fuel system. If you don't hear it, it could be bad or you could have blown a fuse, check fuses first. If you follow the fuel line back from the filter it will lead you to the fuel pump, you can put your hand on it to see if you feel any kind of vibration if you don't hear the ticking. It could be getting weak.

 

[lantraxco]

Look for banjo bolt fittings on the suction side of the fuel system, pull the bolts out one at a time and check for one that has a tiny suction screen in the hollow center of the bolt. Not sure if Kubota used them, but have seen them on several different Japanese diesels.

 

[John C.]

The banjo bolt strainers are pretty common in Japanese machines. You might also check to see if there is an in line fuel filter somewhere. It looks just like what we used to put in cars. Those are for gas and the filter is made of paper. The ones made for diesel are made of brass and can be blown out putting air to the outlet side and blowing back through the inlet side.

 

[Farmer Brown]

@Tags Thanks for your response! I can hear the fuel pump and it sounds consistent as far as the sound it makes it doesn't appear to slow down or speed up. I haven't taken any lines off to ensure this flow is steady. I haven't blead the system simply because when I researched how to change the fuel filter it was only recommended that the fuel shut off to the fuel sediment bowl (a clear see through bowl with a red ring that floats when water is present) then to wipe down the area around the filter prior to removing the old filter, then to fill the new filter with clean fuel and reinstall filter. Next turn the sediment bowl shut off back on and to turn key switch on for a few seconds before trying to start the engine. This was the prescribed way I found to "Prime" the system after fuel filter change and sediment bowl clean out. I cannot find a procedure online for actually bleeding the fuel system. Thanks for your quick reply and any further assistance or recommendations are appreciated.

 

[Farmer Brown]

@lantraxco and John C.
I have pulled the parts schematic for the fuel system for this machine up online and according to Kubota's drawings that I found the prints have print item numbers for replacement purchases etc. There is a total of two filters. (not counting the sediment bowl) One it actually a strainer that is at the fuel tank entry. I would actually call this a fuel strainer rather than a filter but okay whatever....Potato, potatah. The other is the actual metal screw on filter. It is like the oil filter but smaller and silver with Japanese writing on it. If there is another Kubota failed to show this in their documentation. If you have a photo or a drawing of what a banjo bolt looks lke this may help if they have failed to show this and it actually has one.

 

[lantraxco]

Would be #090 in this diagram, there may be others, or not, doesn't show a strainer so maybe not an issue:

https://www.messicks.com/ku/85160?sectionId=217813&diagramId=345540

 

[John C.]

A banjo bolt goes through a hose adapter and will have the mini strainer inside the bolt itself. You can also disconnect the fuel line from the injection pump and run it into a can or bucket. Turn on the key and fuel should run into the bucket at a healthy rate.

 

[Delmer]

The water separator is there to remove the sticks and rocks from the fuel before it gets too far into the fuel system. The banjo bolt screen will be on the intake to the transfer pump, so downstream from the water separator, and shouldn't ever see sticks and rocks if the water separator screen is intact. If you don't have a screen INSIDE that banjo bolt, and you don't have a small inline filter added by somebody along the way, then the next suspect would be the water separator gasket, or any rubber hose in the suction side of the fuel system, but I'd think this was clogged rather than sucking air, because the rubber should be in good shape still on this one, not that old.

 

[56wrench]

I encountered a steel-braided suction line failure years ago. There was no leak but the inner rubber layer would collapse and not allow full fuel flow from the tank so therefore i am always suspicious of any flexible lines in the supply side of a fuel system

 

[Simon C]

I encountered a steel-braided suction line failure years ago. There was no leak but the inner rubber layer would collapse and not allow full fuel flow from the tank so therefore i am always suspicious of any flexible lines in the supply side of a fuel system

If you take rags an make it into a ball the size of a softball and put it over the tank filler neck with a 1/4 inch blow gun pipe slipped under the rag ball. You can have someone put continuous air into the tank and check for fuel leaking out somewhere. It only takes about 1 PSI of air in the tank to show up as a leak on the supply side of the fuel injection pump. If the person is to eager putting air in the tank it willl want to spray or mist out of the rag he or she is holding over the tank filler neck. Good to wear safety glasses when doing this trick. Also great for assistance in bleeding fuel systems. Simon

 

[Farmer Brown]

I'll try this as the weather permits. Thanks Simon C!

 

[Zed]

How did you go? I had a breakdown on a Kubota SVL75 the other day and it was running for a minute or so then engine would die. leave it 5 minutes then it would run but again a minute later die. I checked the fuel water separator and the filter element in there was nearly blocked solid. Looked ok from the outside, but I could hardly blow air though it it. I was out bush so i washed it repeatedly with brake cleaner and then blowing it out each time with compressed air until I could blow through it easily.

 

[Zed]

You mentioned taking the fuel/water sediment bowl off, did you check the filter in there, or was it in there? There should be a spring in the bottom of the bowl to hold element in place. That one I did was proper blocked up with real fine dirt. The fuel system shouldn't need priming, open the fuel tap on the separator housing and then turn on the key and you should see it pumping fuel through.

 

[Farmer Brown]

The issue was found and fixed! I had a blockage in the fuel tank itself. I had previously tried blowing out the fuel line coming from the tank before but still had the problem with it cutting out once the controls were activated. I took apart and checked every fitting etc. all the way up to the injector pump itself to no avail. Changed the fuel pump and that didn't fix it, so I ran a temporary fuel line straight to the the fuel separator from a 5 gallon diesel tank (set it up high on the back above the motor). It ran perfect! Lesson learned: Even though it appeared to be getting sufficient fuel supply from tank when running it actually was starving for fuel. That's why it was cutting out when trying to use the controls or to travel. When I would let off the controls and it would recover and I would move the controls once more and it would start to sputter and die out. When I by-passed the tank and fuel line from the tank and it ran perfect I then knew that the fuel line coming from the tank had some sort of stoppage so I removed the fuel cap and used compressed air to blow back into the tank. This finally cleared it and the problem hasn't returned. (I still need to remove the tank and clean it out at some point).
Hope this helps someone out with their issue. Do the fuel tank by-pass straight to the fuel separator first and this will tell you if you have a fuel supply issue at least up to that point.

 

[Zed]

Great to hear you got it sorted

 

[Welder Dave]

Kind of related but I forgot to put the fuel cap back on my Kubota powered skid steer and lost it. Looked online found another one. Put it on and engine would run then die. Supposedly vented cap wasn't venting. Went to a different vendor and got a Stant cap and problem solved.