B7500 fuel starvation

[drewzee87t]

Tractor stalls out and not stay running. This happened while I am out in a field (yay). Luckily not too far from shop, but not the best work environment.

Will restart, but then stalls out quickly.

I have good clean fuel in tank (just filled in fact).

Checked air filter which has maybe 20 hours on it and it's pretty clean.

I had a fuel filter that I hadn't installed yet, figured that was it. The old filter was absolutely disgusting and there was tons of carp in the bowl. Cleaned all that out really good, put in new filter. The old filter did not have any O-rings installed (and it didn't leak). I did have the O-rings with the new filter. The small o-ring is obvious, but the manual is not clear about he larger o-ring. There is a groove on top of the filter that it slips right into. I put it there. I didn't see where (or why) it would go "under" the filter.

Re-installed filter and bowl and it doesn't leak. Let the filter fill up with fuel and tractor starts, runs for about 10 seconds and dies.

I watched the filter bowl and it fill up after stalling. When you start it gets running perfect, then the fuel level falls below the filter and it sucks air and dies.

I have a new fuel tank lid, but I did loosen it in case it's not venting. No difference.

I disconnected the main fuel line and it's dumping tons of fuel. Just in case, I blew it out and there are no restrictions. I am at this point completely soaked in diesel and have about a gallon in a bucket between all these operations.

I figure that the fuel filter body (the "lid" to the fuel filter bowl) must be clogged. Tried to blow that out but couldn't tell if it cleared or not (I am out in a field, using a can of computer duster air and the fuel is dumping all over the place while I try to blow this thing out).

At this point I think there is a restriction or the check valve is busted on the fuel filter assy "body" (the lid with the in and out lines). I can go out and try to clamp off the fuel supply line or jamb a bolt in it to keep from dumping fuel so I can take it apart tomorrow, but I am considering just getting a new fuel filter assembly complete and just quick swap the lines.

Can anyone think of anything that would cause the filter bowl to not fill up fast enough to keep up with what the motor is using? I think I have pretty much narrowed it down to that fuel filter body. I have inspected all lines and can't find any leaks, or splits and they don't look aged or cracked.

The tractor primes up, starts and runs fine but the fuel level very quickly drops off in the filter bowl and once the level drops too far it shuts off.

HELP?

Thanks

There was one other post with a similar issue, unfortunately, like too many people, the member never bothered to post what was found to be wrong or how he fixed it.

I have the part ready to order or call the local (40 miles from me) dealer with the part number, but I think I will have to plug the fuel line somehow and get the filter assembly off so I can see what it's actually doing.

 

[North Idaho Wolfman]

If your getting good fuel flow in and nothing out, then yes you have something in there plugging up the works.

Pull the housing and clean the ports out.

 

[CowboyLawyer]

I'm having a similar problem with my B3300su. Seemed to loose power, then shortly thereafter stalled. With much cranking, it will fire up for 10 to 15 seconds and die. Dealer came out an replaced the fuel filter, but not improvement. They'll trailer it into the dealer tomorrow. I'll post here with whatever the solution turns out to be. I suspect a clogged injector, fuel pump, or something beyond just a simple filter change. 118 hours on the machine. Purchased March 2014. Ran great until now.

 

[alansz400]

Any reason why you couldn't put something like this on to get you back to the shop and figure out if the filter housing is the problem?
https://www.mrostop.com/p550094-don...dccUBw-FS2VCZ7oQnblySL9UIAhWsnJrLzxoC7yLw_wcB

 

[Bulldog]

Does it have a fuel shut off at the filter base?

Fully open?

 

[drewzee87t]

Okay, so I had a job today. I got to it a little while ago. I clamped off the fuel lines, removed the stupid filter assy and took it to the shop. It was clogged with what appears to be dried grass. I cleaned it out, blew it out, made sure it was all good. Great.

Not great. I went to reinstall it and was very careful. The middle small nipple (return line) broke the F off. I would really like to meet the jerk that came up with this stupid contraption.

I am 100% sure this was the problem. Now I need a new complete assy, which as it turns out, costs about $5 more than the replacement filter and O-rings. I don't see any reason why anyone would even bother replacing the filter. Just replace the whole stupid thing.

So I either have a trip to dealer or wait for UPS. I bet the dealer has tons of these POS on the shelf. I will have it running tomorrow if I can get out early enough to get there.

WHY?

I am just slightly extremely frustrated with this extremely STUPID design.

OK - so to our other viewers, just replace the whole thing and be done with it.

Thanks

 

[67Truckin]

Kubota is a great tractor but they have some really stupid design ideas on them. I have the notorious leaking fuel tank on my BX1800. They simply cut the hole too big by 3/8" or so and have spent years and 4 upgrades trying to fix it. It's hidden underneath the ROPS mount for some dumb reason. Hope you get it all working again!

 

[North Idaho Wolfman]

I went to reinstall it and was very careful. The middle small nipple (return line) broke the F off. I would really like to meet the jerk that came up with this stupid contraption.

Kubota is a great tractor but they have some really stupid design ideas on them.

I will completely disagree with both of you, I've worked on quite a few tractors, and Kubota's are extremely well designed and have been for many a year!

 

[chim]

We have a Volvo tractor at work. Not the kind of tractors we talk about here, it's an over the road tractor for pulling trailers. It had been at the repair shop several times because it would lose power running down the road. Then it would run OK for a little, then lose power again. We took it to a second shop and they couldn't figure it out either. When it was back at the first shop for the umpteenth time, the mechanic discovered a hole in the pot metal base for the fuel filter. It looked like something just ate through the metal. After many weeks of chasing the problem it was finally solved.

 

[Tx Jim]

I'll bet Kubota doesn't build the fuel filter assembly as I've seen other brand tractors with very similar fuel filter assembly.

 

[drewzee87t]

I will completely disagree with both of you, I've worked on quite a few tractors, and Kubota's are extremely well designed and have been for many a year!

I don't think it's particularly good design to put a valve in the fuel flow that's subject to gunking up, however, the fact that a 15 year old piece of plastic broke off doesn't really surprise me and the new filter was cheap. Not trying to slam Kubota nor do I think the other poster was. Stuff is frustrating, regardless what color it is.

At any rate, I put the new filter assembly on and it started up, stalled, then on the third try it kept running.

I ran it for about 10 minutes at 1500 rpm - was running perfectly normal. Shut it off, cleaned up, double checked for leaks, put away tools. Started right up when I came back. Thought I had it licked. I powered up my brush hog and as soon as I went about 3 feet it slogged out and started losing RPM. I clutched and took the PTO out. It RPM was bouncing up and down for a couple minutes and died. Same situation I originally started with. It will start and die, or run for a few seconds and die.

WSM says there really isn't a need to bleed the injectors by cracking the lines open. The new fuel filter is full, no bubbles or anything and the fuel appears to be nice and clean with no indication of water.

I disconnected the hose between the lift pump and injection pump and cranked and the pump appears to be cycling as it should and was squirting fuel out in rhythm with the cranking of the engine.

Tank is still about 1/2 full per the fuel gauge. Air cleaner definitely not culprit, I started it without the cleaner and it behaves the same. Fuel used is from my farm tank. It is probably 6 months old, but I have run about 20 gallons of it through this tractor with no problems and my truck runs on it with no problems. I am pretty sure my fuel supplier puts treatment in it to keep bugs and anti-gel. Most people around here have 300 gallon tanks and don't have any problems with the fuel from this supplier (MFA). I still have probably 70 gallons in the tank, so it's not at the bottom of the barrel.
Tank has filter and water separator.

I am completely stumped and would appreciate any further advice for troubleshooting. I was able to move the tractor about 15 feet, at least got it out of the tall grass and onto my lawn.

Please recommend next steps......

Thanks

 

[mendonsy]

I had a somewhat similar problem a while back. The plastic fuel return line from the injectors to the pump had a very small split in it and was drawing air. The only way I found it was a small spot of fuel on the side of the hose.
Might be worth checking that.

 

[drewzee87t]

Hi

Can you clarify you are talking about the rubber hose between mechanical lift pump and the injection pump? I examined that and I also removed it in order to verify mech pump working correctly. Didn't see any problems, but it's got fuel all over it now

Easy enough to replace but I don't think that's it.

Keep the suggestions coming though. Thanks for quick response

 

[BAP]

I will completely disagree with both of you, I've worked on quite a few tractors, and Kubota's are extremely well designed and have been for many a year!

Actually, it is a dumb design that Kubota builds tractors without a shutoff valve at the bottom of the tank so you can remove any component of the fuel system without loosing fuel. Most other tractor brands have them.
As far as the OP's problem, I just went thru the same thing with my father's B7500 and it turned out to be the lift pump was weak. The dealer kept saying they have never replaced one before, but a new lift pump cured the problem. The old one looked like it was working, but was not pumping enough to make the tractor run right. Tractor runs good now.

 

[drewzee87t]

Mendosny was very close. It was not the return line from the injector to the IP, it was the return line from the IP to the fuel tank. I clamped it off and it runs. I temporary put blockoff plugs at the tank and at the main fuel input for the IP. Will post pics later. The hose was old, but I cut off the hard ends and re-installed it and it still would not work.

There must be a check valve at the banjo bolt thing that connects the fuel line from the lift pump to the IP where it prevent air from getting back in from the tank return. I am guessing not good to run too long as it might overwork the lift pump. I will post pics in a while after I clean this up.

Thanks again everyone! If this don't solve it then it's time for a new lift pump.

Pics added

Does anyone know if there is a check valve at the IP where the return to the tank is. No indication from WSM. If it's not a check valve then probably the lift pump is failing and allowing it to suck in air between strokes.

 

[mendonsy]

Hi

Can you clarify you are talking about the rubber hose between mechanical lift pump and the injection pump? I examined that and I also removed it in order to verify mech pump working correctly. Didn't see any problems, but it's got fuel all over it now

Easy enough to replace but I don't think that's it.

Keep the suggestions coming though. Thanks for quick response

On my B7500 there is a steel line that connects the 3 injectors which ends in a short hose that goes to the top front of the high pressure pump. That short line was a plastic material and had a very small split in it. I replaced it with a 6" length of rubber fuel hose that I purchased from the dealer. I can see that hose in your 3rd photo to the right of the 3 injector lines.

 

[drewzee87t]

after you posted to check the return from injector in IP, I went out and looked at that particular hose and it was fine. That got me thinking where else air might get in, so I checked the hose that I have pointed out. Had my wife crank the thing while I pinched off that hose and it ran fine. Let off the pinch and it died. Did that several times and as long as I pinched off that hose, it ran fine. For whatever reason, that hose is introducing air - I suspect a check valve is in there and not working correctly but there is no info in the manuals.

Thanks again, though - you got me to the right places to look.....

 

[North Idaho Wolfman]

No check valves, so most likely you have a bad pump.
The vent / return lines should all flow fuel back to the tank because of positive pressure from the fuel pump, except for the one off of the filter housing, which should just allow the air to vent out of the filter housing.

 

[drewzee87t]

THanks Wolfman.

I suspect that's hopefully the final bullet in this corpse. I was able to get it back to the shop and so I am in better space to do stuff. I let it charge up the battery for about 20 minutes at 1500 RPM. After that, I ran it up to PTO speed (under no load) 2600 RPM and I noted that the fuel filter bowl was starting to get air in it. It runs with half of filter exposed to air in the bowl at 2600 no load. I suspect once I put load on it, it's gonna choke again. Tank is at a little less than half full now.

Fuel pump is $89 or so. I don't like throwing money at problems, but I can't see what else it could be at this point. That line that I blocked off (the return at the fuel tank 16271-95690 JOINT EYE - which I incorrectly refer to as banjo bolt on the IP) should be getting enough pressure if there is no check valve, that it would always be pushing fuel under pressure to the tank. If that's the case I think I need a pump and be done with it.

THe only other thing I think it could be is if the tank is really clogged up, but I Have already checked that for flow. I won't be surprised to see a few stray bugs or grass pieces in the bowl in the future, but that line is flowing full blast.

Any other ideas before I make a third trip to the dealer on this issue?

Thanks so much for your help!

 

[drewzee87t]

Update, new fuel pump installed. The only thing that has changed is that the filter bowl does not get air in it anymore, it stays full. Unfortunately, the tractor still won't stay running for more than like 20 seconds or so.

I did get some hose to replace the fuel return hose I had blocked off and that problem remains the same - If I don't have that blocked she will not run at all, just sputters and will catch for a couple seconds. I re-blocked that off. I did note that with the new fuel pump, when I went to remove the new hose and re-block it, there were bubbly fuel coming out instead of fuel under pressure.

I am probably close to empty on the tank right now as I was intending to run her out of fuel and then try to blow/flush/vacuum the tank to get anything that might be in there. The lower the fuel level gets the worse it runs. Yesterday with old pump still installed I had her going for 5 to 10 minutes at a clip before dying and getting progressively worse.

I would appreciate logical suggestions for the next, and cheapest, things to check here.

My plan right now:

1. Replace fuel hose from filter to lift pump and hose between lift pump and IP
2. Replace all the small fuel hoses between injector rail and IP, injector rail and fuel tank. I have the setup for a lower serial number B7500 with three separate returns at the fuel tank. The newer serial numbers have a tee fitting between the injector rail to tank return connecting to the JOINT EYE (IP fuel input) and only two returns on the tank (one for the return from pressurized fuel, the other from fuel filter).
3. Check
4. Empty fuel tank out, blow out/clean/vac
5. Fill with about a gallon and check
6. If no love, fill tank over half full and check. This to see if gravity feed will overcome my nice new fuel pump and allow tractor to run, which would indicate that I have a worn out lift pump cam on the fuel injector camshaft. I also benched the old fuel pump and it may be weak, but it pulls vac and outputs pressure when you operate it by hand.

7. LOTS OF HARD ALCOHOL if no love

Please experts, chime in here. It runs fine when it's getting fuel but somehow it's getting air, or perhaps the bottom of the tank fuel is really bad? Should I dump the fuel and get some fresh from somewhere else before I do all the other stuff? I feel like it's just sucking air from somewhere that I can't seem to find.

Thanks again for all your help