B7800 switch? Issue

[ssullivan]

B7800 would not start. Good fuel flow to injection pump. No fuel at injectors. Heard fuel shut off solenoid click when key turned to run position. After removing solenoid I figured out that the key switch would reactivate the solenoid to the off position when key turned to the start position. Installed new switch, all good for 4 to 5 starts. Now I have the same issue. Seems that the new switch is doing the same as the old one.
Any thoughts on this problem?

 

[Dave_eng]

B7800 would not start. Good fuel flow to injection pump. No fuel at injectors. Heard fuel shut off solenoid click when key turned to run position. After removing solenoid I figured out that the key switch would reactivate the solenoid to the off position when key turned to the start position. Installed new switch, all good for 4 to 5 starts. Now I have the same issue. Seems that the new switch is doing the same as the old one.
Any thoughts on this problem?

Henro is the guy who seems to be able to keep this model and its safety systems straight. It seems the B7800 and B2410 are near twins except for some safety systems.

You need to determine if your machine has an OPC for Operator Presence Controller.

It will be located as shown.

How many wires come out of the engine stop solenoid.

You really need a 12 volt test light to troubleshoot your tractor. they are less than $20 at any auto parts store.

Does your stop solenoid have one or two terminals?

Likely there was nothing wrong with your key switch. the problem lies elsewhere.

Please report back once you determine if you have an OPC.

Why it gets complicated is because some engines power the stop solenoid to allow the engine to start while others power the solenoid for about 10 seconds to stop the engine.

Dave

 

[ssullivan]

Is the OPC, 060 in the diagram?
The solenoid has two wires.
I have a test light.
I can start the machine when I remove the solenoid from the equation. Turn off with manual shutoff.
The reason I mention the switch is that before I installed the solenoid and after I put the new switch on I observed the solenoid working properly. After a few starts and I had the same problem I then removed the solenoid and it was doing the same thing, which was as follows.
Solenoid plunger ‘out’ in off position, plunger in when switch in on position and plunger ‘out’ when switch in start position.

 

[Dave_eng]

Is the OPC, 060 in the diagram?
The solenoid has two wires.
I have a test light.
I can start the machine when I remove the solenoid from the equation. Turn off with manual shutoff.
The reason I mention the switch is that before I installed the solenoid and after I put the new switch on I observed the solenoid working properly. After a few starts and I had the same problem I then removed the solenoid and it was doing the same thing, which was as follows.
Solenoid plunger ‘out’ in off position, plunger in when switch in on position and plunger ‘out’ when switch in start position.

There are clues in what you describe. Yes 060 is OPC.

The solenoid has two internal coils. A strong one called the Pull in coil which moves the solenoid plunger initially and a second less powerful coil called a Hold coil.

The Pull in coil should be powered in the key START position. The Hold coil is powered in the ON or run position. If the Pull in coil is not getting power the engine cannot start on the hold coil.

Dave

 

[ssullivan]

Dave,

I purchased a new switch which performed exactly as you described for 4-5 starts. After a no start I pulled the solenoid and it was not ‘pulling’ in on the START position but was holding in the ON position. What is your suggestion on the next step?

Steve

 

[ssullivan]

Dave,

It does have an OPC, part number 6C190-55515

Steve

 

[Henro]

Dave,

It does have an OPC, part number 6C190-55515

Steve

I do have a B2910, which is physically the same as the B7800, but does not have an OPC so it is not the same.

Looking at the diagram Dave posted, your fuel cut off solenoid has both coils hooked in parallel, so they operate together, when the OPC energizes the (2) key stop solenoid relay.

Since we do not know the logic within the OPC, we can only assume the solenoid is either always energized when the tractor is running, or that it is only energized when the tractor is shut off, to cut fuel off until the engine stops. Has to be one or the other.

What I probably would do is first pull out the key stop solenoid relay and see what happened. If the tractor still does not start, this would indicate that the fuel cut off solenoid is likely energized to keep the tractor running, and deenergized to shut the tractor down. I guess you could accomplish the same thing by unplugging the fuel cut off solenoid if that is easier.

(Of course, simply checking voltage applied to the solenoid would also give a clue as to what is happening.)

With the relay out of the circuit, and if the tractor did not start, I would apply 12 volts to the solenoid directly, and see if the tractor started. If so this would prove the issue is not the solenoid and something else. And prove that you need 12 volts applied to the solenoid for the tractor to run.

Which would mean, either the key stop solenoid relay is bad, or the OPC is not telling the key stop solenoid relay to energize. The root cause could be a bad OPC or something going on in the switches feeding info to the OPC.

So after all that, what could the root problem be?

A bad OPC
A bad key stop solenoid relay
A bad fuel cutoff solenoid
A bad switch feeding the OPC information (8,9,10,11,12)

The clutch switch would only come into play if the starter does not turn the engine over, but it sounds like your engine turning over.

Try to get some measurements/more info and report back. OPC modules are expensive I believe so you don't want to buy one if you do not need it.

Hope this helps...

Also, you may find a B7800 workshop manual at kubotabooks.com for free or a small donation to the site.

edit: the key switch could also be the issue, but unlikely, since you already replaced it and it functioned until the issue reappeared. Also a wiring problem could be there, but one step at a time...

 

[Dave_eng]

I need to read through all the info posted again.

The parallel coils in the wiring diagram have always puzzled me because I have seen Kubota wiring diagrams where there was an internal switch inside the stop solenoid. This switch opened once the stop solenoid plunger moved thus leaving the Hold coil as the only one powered.

An ohm meter could be connected between the power wire for the solenoid and the case of the solenoid. If the reading changed significantly when the plunger was moved it would reveal the presence of an internal switch.

Study these photos closely.

The tractor's wiring diagram shows the two solenoid coils connected to one external wire just like the B7800 wiring diagram shows and no internal switch is present.

The section of the WSM describing testing the stop solenoid (remember this is the same tractor and same stop solenoid) shows an internal switch which opens as soon as the solenoid plunger moves.

The actual testing procedure for the same solenoid cautions about powering the pull in solenoid for more than two seconds during testing.

My point in all of this is I think the wiring diagram I have posted for years for the B7800 is misleading as there may well be an internal switch present.

If there is such a switch it dramatically changes the troubleshooting.

Dave

 

[Henro]

Dave said:

My point in all of this is I think the wiring diagram I have posted for years for the B7800 is misleading as there may well be an internal switch present.

If there is such a switch it dramatically changes the troubleshooting.

I remember reading a post here somewhere, where the poster commented something about his solenoid having an internal switch.

If this is the case, then logic would seem to say that such a dual coil solenoid would normally be energized for the engine to run, and deenergized to shut the engine off.

The thought being that the once the solenoid armature was moved to the "ON" position, the pull in coil would be deenergized by the internal switch, and the hold coil would keep the solenoid in the "on" or "run" position, until voltage was removed.

So if the solenoid is getting voltage, if the internal switch failed, it would not move into the run position, and the tractor would not start.

A good first check for the OP would be to see what the voltage on the wire feeding the fuel cutoff solenoid is doing when the key is turned to the run position. My guess is that voltage should be applied to the solenoid by the OPC module when the key is turned to the start positon, and then voltage would be maintained until the key is turned to the off position. BUT remember, I said guess. No specific knowledge of the B7800...

 

[PoTreeBoy]

Thanks Dave. I've suspected such a solenoid existed, but wasn't sure. And thanks for the troubleshooting procedure. What model did you get the figures from?
Somebody needs to post a sticky on the different solenoids, part numbers, the troubleshooting procedures, and which tractors have which solenoid.