Kubota F3680 Engine Stops After Random Intervals

[Deviation]

Hello! I am a new owner of an older F3680 with 1500 hours on the unit. I am having an issue lately where the mower will shut off after mowing for a bit. It seems to be random and it will start right back up and can mow again. It is frustrating! It does not act like it is running out of fuel and have checked the fuel pump, filters, etc. It shuts off immediately like you turned the key off.

I initially thought that the engine stop solenoid was going bad, so I replaced it and it did not help. It doesn't appear to be overheating (and shutting down due to that). I am running out of ideas. Is there a controller or relay that could be going bad on this unit that could be causing this?

Thanks so much for your help! This is my first post, so go easy on me!

Chris

 

[Mark_BX25D]

It shuts off immediately like you turned the key off.

When I read your title, I thought of gunk floating in the tank that periodically blocks the outlet, but this point doesn't seem to fit with that scenario.

Since the fuel stop solenoid is now presumed to be good, check the wiring to it. There might be a flaky connection.

I'd also be looking for a safety switch that is acting up.

 

[Deviation]

When I read your title, I thought of gunk floating in the tank that periodically blocks the outlet, but this point doesn't seem to fit with that scenario.

Since the fuel stop solenoid is now presumed to be good, check the wiring to it. There might be a flaky connection.

I'd also be looking for a safety switch that is acting up.

Thanks, yes, I thought about just running 12v to the solenoid and see if it cuts out. Of course, that would disable all safety switches, so I probably shouldn't mow like that. There is a controller on this unit that controls the solenoid. I thought about replacing it, but it is a $300 part.

 

[MOOTS]

Check your safety switches. PTO, seat and park brake. I've had a 2690 park switch do what you are describing. Randomly dies, and sometimes restarts, sometimes not.

Here's a F3680. Red is PTO switch, Yellow is seat, it has been jumped here to drive unit while torn down. Park switch is under platform near brake pedal.

 

[Deviation]

Check your safety switches. PTO, seat and park brake. I've had a 2690 park switch do what you are describing. Randomly dies, and sometimes restarts, sometimes not.

Sounds good, I will try checking the safety switches. Thanks!

 

[MOOTS]

Sounds good, I will try checking the safety switches. Thanks!

Added a picture above.

 

[Deviation]

Added a picture above.

Thanks, very helpful!

 

[GeoHorn]

Check that your fuel cap vent is open.

 

[kmengarelli]

I know this is an older post, but did you figure it out? I am having the same issue except sometimes it won't start for hours after it shuts down.

 

[kmengarelli]

Sounds good, I will try checking the safety switches. Thanks!

Did you figure out the issue? I am having the same issue. I'm going to replace the oil pressure sensor and temp sensor, and I have checked the pto and brake switches. The seat switch has been bypassed.

 

[Jeff.t7]

My f3860 has been doing this exact issue going on the second season. I’ve taken it to the Kabota dealership and they’ve replaced the solenoid for the fuel pump. They replaced the safety switch in the seat. They don’t know what the issue is. Has anybody actually figured this out yet. Very frustrated.

 

[Jeff.t7]

Did you figure out the issue? I am having the same issue. I'm going to replace the oil pressure sensor and temp sensor, and I have checked the pto and brake switches. The seat switch has been bypassed.

Were you able to figure this out? I am at loss and it’s getting expensive for the Kabota dealership to experiment with parts.

 

[MOOTS]

Were you able to figure this out? I am at loss and it’s getting expensive for the Kabota dealership to experiment with parts.

He hasn’t been on since January ‘24. Probably won’t get a reply.

What exactly is your machine doing?

 

[Jeff.t7]

He hasn’t been on since January ‘24. Probably won’t get a reply.

What exactly is your machine doing?

Thanks for the reply. It doing exactly what they said. It runs for a while and all of a sudden it quits like the key was turned off. Some times it starts and other times it takes several try’s or maybe it won’t start at all. Eventually it starts. May run all day and not quit. If I take it to the shop for them to test it will not quit for them. Kubota has replace random things fuel solenoid, seat safety switch. And the the wiring harness. It will quit when the engine is cool and or quit when it is hot. Bumps while driving don’t seem to effect it. It will quit when the blades running or not running.

 

[MOOTS]

Thanks for the reply. It doing exactly what they said. It runs for a while and all of a sudden it quits like the key was turned off. Some times it starts and other times it takes several try’s or maybe it won’t start at all. Eventually it starts. May run all day and not quit. If I take it to the shop for them to test it will not quit for them. Kubota has replace random things fuel solenoid, seat safety switch. And the the wiring harness. It will quit when the engine is cool and or quit when it is hot. Bumps while driving don’t seem to effect it. It will quit when the blades running or not running.

Yeesh. So hard to diagnose not being there.
Like I posted earlier in the thread, I had a parking brake micro switch act up with me. The lever got bent and the machine didn’t know the brake was off, would die when tried to move forward or reverse. If I’m remembering correctly.
When it shuts down, will it crank to try and restart? Or it doesn’t do anything?

 

[Parksken]

Hi I came across your post and currently having the same issue. Could I ask why the parking brake micro switch cause the unit to shutdown? I could see that could be the case if there is no weight on the seat cause I assume the seat sensor is somehow tied into the parking break. So far I have changed out the seat sensor and wiring, ignition switch, battery, fuel injectors, filters, drained and cleaned the tank, fuel shutoff solenoid, fuel pump. Don’t think it’s the pto switch because the unit will turn over and often starts after 2 or 3 cranks. Sometimes though it seems like the unit requires a cool down (1/2 hour sometimes) before it will fire up. I’m pulling my hair out at this point so any help would be appreciated

Yeesh. So hard to diagnose not being there.
Like I posted earlier in the thread, I had a parking brake micro switch act up with me. The lever got bent and the machine didn’t know the brake was off, would die when tried to move forward or reverse. If I’m remembering correctly.
When it shuts down, will it crank to try and restart? Or it doesn’t do anything?

 

[Mark_BX25D]

Hi I came across your post and currently having the same issue. Could I ask why the parking brake micro switch cause the unit to shutdown?

Simple - it's defective. It is intended to sense when the seat is depressed a certain amount and get it into therapy.

Oh, wait....

Sorry, not therapy. What was I thinking?

It's supposed to shut off the engine because, obviously, if there's no weight on the seat then you fell off (have you been drinking again?). And if you fall off, well, we don't want you to get run over by your own Kubota. (We don't care if your neighbor runs you over with his Kubota, we just don't want you run over with your own.)

I don't know for sure on this model, but generally, these safety switches are designed to break the circuit when you fall off. So, if the switch is going bad, it may break the circuit randomly, thus killing the engine randomly. (Because it thinks you are falling off randomly. You should probably not do that.)


Now, since it's intermittent, it can be very hard to diagnose. One approach was mentioned above:

Thanks, yes, I thought about just running 12v to the solenoid and see if it cuts out. Of course, that would disable all safety switches, so I probably shouldn't mow like that.

The idea is to bypass the switches and see if there is a problem there. But its probably more effective to locate each safety switch, and bypass each one individually, and NOT all at once. One at a time.

Then you drive the beast as normal, and see if the problem persists. Oh, it keeps happening? Move your bypass to the next switch.

Once you are reasonably sure you have found the faulty switch, you replace it.


That's the general idea, anyway. Again, I don't know your unit in particular, so this is the general concept. Find a wiring diagram and take it from there. Holler back here if you have more questions.




By the way, PLEASE do not bypass a safety switch and leave it that way. Do this ONLY temporarily as a diagnostic method.

Those safety switches are there to save your life. Please keep them functional.

 

[Parksken]

Simple - it's defective. It is intended to sense when the seat is depressed a certain amount and get it into therapy.

Oh, wait....

Sorry, not therapy. What was I thinking?

It's supposed to shut off the engine because, obviously, if there's no weight on the seat then you fell off (have you been drinking again?). And if you fall off, well, we don't want you to get run over by your own Kubota. (We don't care if your neighbor runs you over with his Kubota, we just don't want you run over with your own.)

I don't know for sure on this model, but generally, these safety switches are designed to break the circuit when you fall off. So, if the switch is going bad, it may break the circuit randomly, thus killing the engine randomly. (Because it thinks you are falling off randomly. You should probably not do that.)


Now, since it's intermittent, it can be very hard to diagnose. One approach was mentioned above:




The idea is to bypass the switches and see if there is a problem there. But its probably more effective to locate each safety switch, and bypass each one individually, and NOT all at once. One at a time.

Then you drive the beast as normal, and see if the problem persists. Oh, it keeps happening? Move your bypass to the next switch.

Once you are reasonably sure you have found the faulty switch, you replace it.


That's the general idea, anyway. Again, I don't know your unit in particular, so this is the general concept. Find a wiring diagram and take it from there. Holler back here if you have more questions.




By the way, PLEASE do not bypass a safety switch and leave it that way. Do this ONLY temporarily as a diagnostic method.

Those safety switches are there to save your life. Please keep them functional.

thanks for the reply !! changed out the break switch and still no luck... think that i will be forced to tear it down and go wire to wire at this point

 

[MOOTS]

Hi I came across your post and currently having the same issue. Could I ask why the parking brake micro switch cause the unit to shutdown? I could see that could be the case if there is no weight on the seat cause I assume the seat sensor is somehow tied into the parking break. So far I have changed out the seat sensor and wiring, ignition switch, battery, fuel injectors, filters, drained and cleaned the tank, fuel shutoff solenoid, fuel pump. Don’t think it’s the pto switch because the unit will turn over and often starts after 2 or 3 cranks. Sometimes though it seems like the unit requires a cool down (1/2 hour sometimes) before it will fire up. I’m pulling my hair out at this point so any help would be appreciated

With so many new parts thrown at it, might be time for a compression test.
When it shuts off, does it sputter out, or like you turned key off? How long has it been running before shutting off? Consistent or random times?

 

[Parksken]

With so many new parts thrown at it, might be time for a compression test.
When it shuts off, does it sputter out, or like you turned key off? How long has it been running before shutting off? Consistent or random times?

With so many new parts thrown at it, might be time for a compression test.
When it shuts off, does it sputter out, or like you turned key off? How long has it been running before shutting off? Consistent or random times?

No sputtering just straight off. The unit randomly shuts off, could be just sitting idling after working for a few hours or 5 minutes after its started. i have tried to pin it down if rough terrain causing this issue and there hasn't been any commonality. Sometime the machine will fire right back up and other times it can take more then a few attempts to fire back up.