M9000 electrical question

[Fedup]

I'm working on this M9000 cab tractor today, getting a front final drive apart to replace the seals. I'm about done with taking it apart, and I'm getting ready to leave when the guy asks me about this...

When he turns the key on past "on" and onto the glow plug position the fuel shutoff solenoid starts hammering on and off rapidly. Start the engine and turn the key back to "on" and the hammering stops. It starts and runs fine, shuts off with the key with no problem. He has replaced the solenoid as per someone's instructions with no improvement. That's no surprise because I doubt the solenoid is causing the hammering, it's more likely the signal to it that's inconsistent. Question is what would cause it?

Is there a glow plug timer or any tricky stuff in the glow plug circuits that might affect the fuel shutoff? Assuming I will be expected to look deeper into it when I go back, but I'm not really sure where to start.

 

[Dave_eng]

I took a quick look at the electrical systems for a M9000. There are several variations and what follows is a quick reaction not the result of hours of studying the system.

There is a diode electrically located between the two leads to the engine stop solenoid.

Often a diode is used to stop back feeding of a circuit from another circuit or in other words to keep to connected circuits isolated from affecting each other.

The image available from Messicks parts illustration shows a small component but I have not seen one so I cannot comment further.

The diode is located where shown as #080 in the illustration below.

Note the location electrically circuit wise of the diode between the two power leads to the engine stop solenoid.

The above is a quick reaction to the symptoms described. Spending a little time trying to locate the diode and verifying its condition is my best suggestion. Others may have more direct experience with M9000's.

Dave

 

[kubotafreak]

Should be able to use a DMM to test that plug. It looks like a dummy plug, two flat spade connector.

 

[Fedup]

Interesting. Always amazes me how engineers love to complicate things. What ever happened to the simple "power to the coil, engine runs - power is removed, engine stops". I guess that's just TOO simple.

Thanks, I will look at that possibility when I get back out there.

 

[kubotafreak]

I say usually... These are connected to a timer circuit. They(fuel shutoff) also mechanically rest at open. The diode is needed to prevent back flow to the device. Like if you had the machine running, moved the key to off then back on again. It would force the kill time cycle to take place uninterrupted. Be happy the diode is a replaceable $7 diode in harness, then on the $2000 pcb that is inaccessible.

 

[Jim L.]

Looking at the diagram that Dave posted, there appear to be four devices with coils grouped.

As kubotafreak points out the diode is there to control current flow.

As the coils are fed power and disconnected, they release energy back into the circuit. This can lead to "dueling relays" which give a characteristic chatter.

Diodes usually fail totally open or totally shorted. Easy to test with a VOM.

 

[Fedup]

Probably easier to test than to find. The diode in question is in plain sight on the diagram, but what about on the tractor?

 

[Dave_eng]

If, when you look at the tractor in the area marked in the parts illustration and cannot find it, take some photos and post them,

None of us from what I hear/read has actually had anything to do with such a diode on a M9000

The diode costs $16.63. Part number 36330-75390

If you have a dealer close by, visit them with your tractor serial number and ask if they can tell you if your tractor actually has such a diode.

As I said in my first post, there are several variants of M9000 and each has slightly different wiring arrangements.

Messicks parts system says that diode is used on 99 different Kubota models.

Further, the involvement of this diode with your issue is just my best guess.

Investing $16.63 to buy a part to help you find it on your tractor is not unwise when you consider the cost of having a tech visit and diagnose the problem. Electrical troubleshooting is difficult and time consuming and going through a few hundred $ in labor would not be uncommon.

We will all continue to try and help as best each of us can.

Dave

 

[kubotafreak]

Probably easier to test than to find. The diode in question is in plain sight on the diagram, but what about on the tractor?

The diagrams are pretty accurate, given the exploded nature of the picture. Just look above and to the right of the starter. The diode terminal will be yellow or white. and taped to the main harness. It looks like a dummy plug.

 

[Fedup]

As I recall, the starter would be pretty much behind the loader framework, but I didn't actually open the hood and look back there at the time. Some things improve with age, but eyesight isn't one of them. Sometimes I have a hard time spotting small objects in a dark area, particularly when I'm not sure where to look or what I'm looking for. I will certainly give it a try when I get back to it. If it turns out that the diode is his problem, it would be a simple fix.

 

[MrMetts]

Probably easier to test than to find. The diode in question is in plain sight on the diagram, but what about on the tractor?

I know I'm late to the party here, but I'm wrestling the very same issue on my M6800. The engine starts, but sometimes dies a couple of times before running steady. It shuts off normally with the key. The diode in question is located under the dash on my tractor. It's bright yellow and taped to the outside of the wiring loom with blue tape. It's in plain sight once you take the top off the dash. My diode tests OK and I get full battery voltage on the output side of it. But I only get about 6 volts on the small wire that plugs into the fuel shutoff solenoid when the main switch is in glow position. When the diode is unplugged, the chattering doesn't occur, but the engine won't start either. I've studied the wiring diagram for hours, and tested everything I can find to test. I can only conclude that in my case the wire is shorted or almost broken somewhere between the diode and the solenoid. I've replaced the solenoid and the timer with no change. My next step will be to run a jumper wire directly from the diode to the solenoid to see if that fixes it. If anyone finds a fix, please post it!

 

[1952seb]

The diode was the fix for our M9000. Several years ago we had the rapid clicking issue. We had to replace the shut-off solenoid twice- very expensive, & neither stopped the clicking. No mechanic or parts guys I talked to knew what the problem was. I finally found a mention of the diode on a forum.
There are actually 2 on our M9000- one is just behind the battery (L side) taped to a wire harness with some other wires. We tried it first; no luck. The second is behind the alternator off the wire harness; this one fixed the clicking.
Now it's about 3 years later & the clicking started again. First we tried the alternator diode; no luck. I couldn't remember where the other one was, so that's what brought me to this forum thread. It's not shown on the schematics at the top, so we followed the harness & found it up behind the battery. Tried it & Bingo! It stands to reason it was the diode that we didn't replace the first time. Due to the current economy, the new diode was $23.

 

[whitetiger]

M9000 Fuel Solenoid Chattering
Document ID GE652
Status Published
Published Date 06/03/2022

Title
M9000 Fuel Solenoid Chattering
Subject
The fuel shutoff solenoid chatters during key on when the glow plugs are activated.
Issue
If power does not reach both terminals of the fuel stop solenoid when the glow plugs are activated, this leads to a chattering effect because the pull-in coil is unable to complete the pull in process without help from the hold coil. This is caused by a defective diode in the circuit, which can be confirmed by jumping both fuel stop terminals together and then operating the glow plugs. If the chattering ceases, the problem is the diode with part number P/N 36330-75390. If the diode shown in the parts breakdown is not the issue, please see the picture below for the location of another diode that can be difficult to find. It is tucked in by the battery.

Models
M6800, M8200, and M9000
Recently Viewed

 

[Mark_BX25D]

Further, the involvement of this diode with your issue is just my best guess.

I think it's a good guess. As I read your post and saw it, I said, "Bingo!".

Investing $16.63 to buy a part to help you find it on your tractor is not unwise when you consider the cost of having a tech visit and diagnose the problem. Electrical troubleshooting is difficult and time consuming and going through a few hundred $ in labor would not be uncommon.

Fully agreed! Parts swapping is usually not the best course of action, but in this case, we have a cheap, easily replaced part that has a strong possibility of being the culprit. This is one place where swapping a part is a good gamble.

 

[1952seb]

Thank you for that great technical explanation!
After replacing the second fuel solenoid, but before reading about the diode, we had even tried a relay, which did nothing ($100+ and non- returnable). Our closest dealers are 40+ minutes away with long waits to get into, so we try to do everything ourselves. The diode problem has been solved twice now, which was the cheapest, fastest solution. It's to be expected that little 20 year old parts give out.