Bad news big repair

[Hay Dude]

Purchased my M135X in warmer months almost 3 years ago (April 2019). Never thought to see if the glow plugs worked. They actually won’t work if it’s over 41*.
Last winter, I realized the glow plugs weren’t working. Ohmed out wires, looked at wiring for mice damage, water damage, bad grounds, etc. Ohmed out wiring. Thats when I learned the glow plug system in larger kubotas is more complex than I thought. All 4 glow plugs passed electrical testing.
The glow plugs have 2 sensors one for air temp, one for water temp. The ignition switch is also part of the circuit. Then there are 2 relays and a fuse. All of this is controlled by the ECU. Last winter, I replaced
Key switch
water temp sensor
air temp sensor
both relays
fuse

Still no glow plugs. With nothing left to replace or test, I succumbed to a very reputable Kubota dealer. They basically did all the same things I did and replaced one of the new sensors I had already placed.
Still nothing. They called Kubotas double secret probation hotline and Kubota thinks it’s the ECU.

ECU price $6000
ECU Not returnable and no guarantee it will fix glow plugs.

So I’m out of answers. Any thoughts on other possible avenues to pursue?

 

[GSVette]

Not a good answer- how about just continuing to run without glow plugs? Neither my 8.2l Detroit Diesel nor the Cummins BT-4 have them. Yes they are slow to start in the cold and sound like a clattering bucket of bolts until they warm up ( not to mention the clouds of smoke). But they do start and run fine (once they warm up)

 

[dodge man]

A used one or rigging up some kind of switch on your own.

 

[Hay Dude]

Not a good answer- how about just continuing to run without glow plugs? Neither my 8.2l Detroit Diesel nor the Cummins BT-4 have them. Yes they are slow to start in the cold and sound like a clattering bucket of bolts until they warm up ( not to mention the clouds of smoke). But they do start and run fine (once they warm up)

Thats what I’m doing now, but at 25* the Kubota 6.1L gets real angry.

 

[k0ua]

Forget about the ECU. Just manually wire up and manually control the Glow plugs. A simple SPST pushbutton switch on the dash to control the glow plug relay. YOU will now be the ECU. You have a brain. Use that brain to control the glow sequence by turning on the ignition key pressing the button for 15 seconds, start engine, and "post glow" if necessary for a few seconds while the engine is running. Release button. Done. Now wasn't that simple?

 

[Hay Dude]

A used one or rigging up some kind of switch on your own.

ECUs are really unique. Each tractor has its own depending on when it was built and features. Not to say if I found the same tractor built around the same time it couldn’t be possible, but nobody would sell a used ECU from a donor tractor, they would want to sell with engine since engine can’t run without.
I did look around for one, though.

 

[Hay Dude]

Forget about the ECU. Just manually wire up and manually control the Glow plugs. A simple SPST pushbutton switch on the dash to control the glow plug relay. YOU will now be the ECU. You have a brain. Use that brain to control the glow sequence by turning on the ignition key pressing the button for 15 seconds, start engine, and "post glow" if necessary for a few seconds while the engine is running. Release button. Done. Now wasn't that simple?

I don’t think it’s that simple, but yes, the thought crossed my mind. They make timer switches too, so you can’t accidentally leave them on.
The sensors must stay in place. We tried to bypass the sensors and if you bypass them, the engine runs de-rated.

 

[RickB]

Forget about the ECU. Just manually wire up and manually control the Glow plugs. A simple SPST pushbutton switch on the dash to control the glow plug relay. YOU will now be the ECU. You have a brain. Use that brain to control the glow sequence by turning on the ignition key pressing the button for 15 seconds, start engine, and "post glow" if necessary for a few seconds while the engine is running. Release button. Done. Now wasn't that simple?

Probably the best low cost option. It is absolutely that simple. Use adequate sized wire directly from the battery, a properly sized relay and a control circuit from the relay to the operator station. I'd use keyed power for the control circuit.

 

[dodge man]

I’m not surprised a used ecu would be hard to find. It’s easy for me to say rig up a glow plug switch but I’m sure it’s not that simple. 10 seconds is all it takes.

 

[Hay Dude]

Probably the best low cost option. It is absolutely that simple. Use adequate sized wire directly from the battery, a properly sized relay and a control circuit from the relay to the operator station. I'd use keyed power for the control circuit.

The ECU reads the air and water temp sensors and they are both part of the glow plug wiring circuit and it has been stated that if the relays are bypassed, the tractor derates itself.
So how do you bypass all that and “simply install a switch”?

 

[Hay Dude]

I’m not surprised a used ecu would be hard to find. It’s easy for me to say rig up a glow plug switch but I’m sure it’s not that simple. 10 seconds is all it takes.

Yes and I have replaced glow plugs, switches and relays myself. Problem is, this one is part of a pretty complicated set of sensors and is ECU controlled.
One would have to find a way to have the sensors “fool” the ECU that they are still connected for the tractor to run full power.

 

[Jchonline]

Purchased my M135X in warmer months almost 3 years ago (April 2019). Never thought to see if the glow plugs worked. They actually won’t work if it’s over 41*.
Last winter, I realized the glow plugs weren’t working. Ohmed out wires, looked at wiring for mice damage, water damage, bad grounds, etc. Ohmed out wiring. Thats when I learned the glow plug system in larger kubotas is more complex than I thought. All 4 glow plugs passed electrical testing.
The glow plugs have 2 sensors one for air temp, one for water temp. The ignition switch is also part of the circuit. Then there are 2 relays and a fuse. All of this is controlled by the ECU. Last winter, I replaced
Key switch
water temp sensor
air temp sensor
both relays
fuse

Still no glow plugs. With nothing left to replace or test, I succumbed to a very reputable Kubota dealer. They basically did all the same things I did and replaced one of the new sensors I had already placed.
Still nothing. They called Kubotas double secret probation hotline and Kubota thinks it’s the ECU.

ECU price $6000
ECU Not returnable and no guarantee it will fix glow plugs.

So I’m out of answers. Any thoughts on other possible avenues to pursue?

There is a slim chance if a specific capacitor or transistor can be identified as the culprit it can be replaced by an electronics repair shop.

I wonder if you can find an old one on ebay or similar in a junked machine? Probably a long shot.

 

[dodge man]

Are the glow plugs 12 volt or is the voltage stepped up or down? If it’s 12volts just disconnect everything. Jam a wire on the positive side of the battery, put an appropriately sized fuse near the battery, use a push button switch with a spring behind it, and just hard wire to the glow plugs.

 

[GeneV]

A heated garage option available?

 

[RickB]

The ECU reads the air and water temp sensors and they are both part of the glow plug wiring circuit and it has been stated that if the relays are bypassed, the tractor derates itself.
So how do you bypass all that and “simply install a switch”?

Notice I didn't say anything about bypassing sensors or relays. If it doesn't derate now why would it with an alternate power supply for the glow plugs? You did say they aren't getting powered now, did you not?
I know you want to find fault with everything I post and frankly I don't care.
It looks like you have 3 choices.
1. The status quo.
2. A $6K repair.
3. Spend $50- 100 bucks on some decent components and see if I might be correct.

edit: You could also probably install a coolant heater and get by with it.

 

[K5lwq]

I would do as other’s suggested. Leave all the connections connected. Remove the wire to the glow plugs and tape it off. Then wire the switch relay setup you add to the system to the glow plugs. No reason that would not work.

 

[dodge man]

I’ll add when I say disconnect everything, I just mean all the hot wires to the glow plugs.

 

[Hay Dude]

I have considered a direct wire to the glow plugs last year. It’s not a novel approach, but I believe when you disrupt the glow plug circuit it may derate the tractor.
Right now, the ECU is still reading the air and water temp sensors, but something else in the ECU circuit won’t turn them on. When I removed the water temp sensor plug from the water temp sensor in the glow plug wiring harness circuit, the tractor went into a derated mode.
What I think might happen is when the ECU sees the glow plug wiring circuit disrupted it will derate. I don’t know for sure.
I guess there’s only one way to find out…..
If I can fool the ECU into seeing both sensors, it may be possible, but I think any part of the harness not reading causes derate.

 

[LouNY]

I would look at the relays in the existing system. With two relays does each relay provide power to half the glow plugs.
Or does one do preheat and one do after start heat.
You may wish to ohm out the connections to the relay coil to see if one goes to ground constantly or if they are having constant power applied and switching the ground through the ecm.
If they are standard 5 pin relays get some #22 wire and slip it in the relay coil contacts to see if the relays are being activated. You can look for voltage to be applied to either contact of the relay coil if you have voltage on both pins you will know they are switching the ground with the ecm.
Once you know what they where attempting to do run a wire to the existing relay through a switch to either power or provide a ground.
That should allow you to control the glo plugs and get her started much easier and smoother.

 

[K5lwq]

I don't think the computer will know the difference. The wire on the glow plug is after the relay. The computer control ends at the relay.