B7800 HSD won't turn off with Key

[jlmartin102001]

My 2006 B7800 HSD would not start due to battery drained. After charging battery it started but seemed to have some air in the fuel lines since it cranked but would not turn over. Left it sit overnight then it fired up next day and was running fine. Then it shut off but started back up again. However following that episode engine would not stop with key turned to off position. I found the manual fuel shut off switch (older models must have had a throttle like cable that turned engine off). Checked the 5 fuses and replaced the 5 amp Key shut off but nothing. Interesting the 30 amp "Solenoid" was blown but replacing that didn't fix the problem. not sure it that works the starter solenoid and not the fuel solenoid. Took apart the instrument panel to find a mouse nest and several disconnected wires. Fixed them and still didn't work although now my fuel gauge is working so that must have been issue there. looked at other switches for ground issues and didn't see anything easy. I watched you tube clip on issue and they seemed to think it was the fuel solenoid that was bad. Interesting the safety switch for the seat also didn't seem to work since I engaged rear PTO then got up from seat and it didn't shut the PTO off. Any thoughts on this.
thanks

 

[Dave_eng]

I quickly looked at the B7800 HSD shop manual supplement.

It looks like your OPC system (operator presence control system) uses a timer to send power to the engine stop solenoid to stop the engine.

The timer is incorporated within the controller.

This design is in contrast to a system where the stop solenoid is powered to keep the engine running.

Your system uses a timer so that power is only going to the stop solenoid long enough for the engine to stop. Remember, this happens after the key is turned off so without the timer, with the key off power would flow to the stop solenoid until the battery is dead.

I will try and attach the supplement for your study.

My suggestion is to use a 12 volt test light available at any auto parts place for less than $20.

Connect the alligator clip to the battery negative terminal.

Use the sharp probe to test for power going to the stop solenoid.

When you turn the key from ON to OFF there should be a few seconds of power going to the solenoid.

If this is what happens then the next suspect is the solenoid.

Dave

 

[jlmartin102001]

Wow. this is awesome. Thank you.
A few questions

• is the stop solenoid the same thing as the Fuel Solenoid? Do you think it is this part?
• 
• what would the timer look like or is that incased in the switch?

I'm trying to get all the parts I might need since the tractor is at my farm which is in another state.

thanks again

Jeff

 

[Dave_eng]

Wow. this is awesome. Thank you.
A few questions

• is the stop solenoid the same thing as the Fuel Solenoid? Do you think it is this part?
• View attachment 50317
• what would the timer look like or is that incased in the switch?

I'm trying to get all the parts I might need since the tractor is at my farm which is in another state.

thanks again

Jeff

That is the engine stop solenoid or fuel solenoid.

The OPC controller is a small plastic box.

Usually held by one bolt at the top and the wire connectors coming in from below.

Dave

 

[Henro]

I quickly looked at the B7800 HSD shop manual supplement.

It looks like your OPC system (operator presence control system) uses a timer to send power to the engine stop solenoid to stop the engine.

The timer is incorporated within the controller.

View attachment 50318

This design is in contrast to a system where the stop solenoid is powered to keep the engine running.

Your system uses a timer so that power is only going to the stop solenoid long enough for the engine to stop. Remember, this happens after the key is turned off so without the timer, with the key off power would flow to the stop solenoid until the battery is dead.

I will try and attach the supplement for your study.

My suggestion is to use a 12 volt test light available at any auto parts place for less than $20.

View attachment 50316

Connect the alligator clip to the battery negative terminal.

Use the sharp probe to test for power going to the stop solenoid.

When you turn the key from ON to OFF there should be a few seconds of power going to the solenoid.

If this is what happens then the next suspect is the solenoid.

Dave

Dave,

My B2910 is essentially the same tractor as the B7800, so this thread caught my eye.

How did you determine the fuel cutoff solenoid is only powered when the engine is to be shut off, rather than powered all the time, to be de-energized when the engine is to be shut off?.

Just curious, as my BX2200 fuel cutoff solenoid is similar, in that it has two coils, but one (hold coil) stays energized all the time the engine is running. The engine shuts down when power is removed from the hold coil. I see in the B7800 drawing both coils are hooked in parallel, so they act in tandem at all times.

Granted, the system could be designed to work either way.

The OP said replacing the blown 30 amp fuse did not fix the problem. But he did not say if he checked the replacement fuse to see if it failed again.

Logic seems to indicate voltage is needed at the fuel shutdown coil to stop the engine as you stated. So I am just wondering if you have some insight into the inner working of that control module I suppose...

 

[Dave_eng]

Dave,

My B2910 is essentially the same tractor as the B7800, so this thread caught my eye.

How did you determine the fuel cutoff solenoid is only powered when the engine is to be shut off, rather than powered all the time, to be de-energized when the engine is to be shut off?.

Just curious, as my BX2200 fuel cutoff solenoid is similar, in that it has two coils, but one (hold coil) stays energized all the time the engine is running. The engine shuts down when power is removed from the hold coil. I see in the B7800 drawing both coils are hooked in parallel, so they act in tandem at all times.

Granted, the system could be designed to work either way.

The OP said replacing the blown 30 amp fuse did not fix the problem. But he did not say if he checked the replacement fuse to see if it failed again.

Logic seems to indicate voltage is needed at the fuel shutdown coil to stop the engine as you stated. So I am just wondering if you have some insight into the inner working of that control module I suppose...

Henro

The printed material is often contradictory.... in one place is says or shows one thing and in another place it is a different story.

I am making reference to pictures and descriptions of the the solenoid is in the WSM B7800HSD supplement. The supplement is not too many pages but I assume it exists to highlight the differences between the B7800HSD and the B29XX models.

The B7800HSD wiring diagram shows a solenoid with one internal coil with a set of electrical contacts.

The OPC description in the same WSM supplement shows a solenoid with two internal coils.

Lots is left to the imagination and for me it is recalling the systems on a number of tractors and trying to fill in the missing pieces in one particular WSM that forms some of the thoughts I put forward.

You will recall owners who were of low body weight complaining that their engine was often cutting out when they were going over bumps and on slopes because not enough weight was being pressed down on the seat switch. In this particular tractor, the OPC controller incorporates a one second delay timer to not have an engine cut off signal leave the controller so that these annoying engine cut outs are minimized.

I do not have an explanation for why on some engines Kubota powers the engine stop solenoid to keep the engine running while on other engines they power the solenoid to stop the engine.

In this particular thread the initial complaint was that the owner could not stop the engine with the key switch. For the stop systems which need power for the engine to operate the symptoms are more typically I cannot start the engine.

Dave

.

 

[Henro]

Dave, thanks for the reply.

The initial drawing you posted shows the key stop solenoid relay is supplied voltage to operate by the Controller. A 30 Amp fuse feeds the relay contacts which activate a solenoi, which must be the fuel cutoff solenoid.

The OP needs to get back with the information whether the 30 amo fuse opened again after he replaced it.

My guess is that the 30 amp fuse blew again, and the issue is a shorted or grounded coil in the fuel cut off solenoid. Could also be a grounded wiring issue too...

looks like there are two common scenarios: power applied to shutdown or power removed to shutdown. Looks like the B7800 falls into the power applied to shutdown category.

Time for the OP to give further information. But might be difficult for him as he said the tractor is in a different state.

Also, my B2910 does not have a seat presence switch, so maybe I also do not have a operator presence controller(hope so).

 

[Dave_eng]

Henro

I was wrong on one point I need to correct.

The so called solenoid I marked up with a green line is actually a relay which feeds the real solenoid which has two internal coils.

The real solenoid's two internal coils are fed by one wire or circuit.

Sorry for the misinformation!!

Dave