Bad news big repair

[K5lwq]

I thought of trying that last year, but I ran it by someone who was an electronics tech in the military and he thought it would not be a good idea since the tractors have different programming.

I was thinking of not even trying to start it but just cycling the glow plugs to see what happens. Probably not a good idea but it would be tempting.

 

[PhilTheFarmer]

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?

I'm thinking that by-passing all that complicated sensor stuff and just having a direct feed and a manual switch from the battery to the glow plugs might be worth investigating.

Or, if you're worried about forgetting that the manual switch is still 'on' whilst running the engine, add a timer relay that puts power into the glow plugs and drops the power after a preset period of time.

Good luck with the repair - I wouldn't contemplate changing out the ECU for that money!

Phil

 

[LittleBill21]

Here is a thought. What if you tried the ECU out of the M126X to see if it would fire the glow plugs? At least then you would know if there is a problem with the ECU. Of course if it blows the glow plug circuit you will need two bypass switches. But that is cheap enough.

or it could be tested in about 5 minutes with a multimeter, with 0 risk

 

[JimRB]

I see the thread has devolved into the same options repeated often. If your wiring diagram is like the one I posted, have you confirmed the voltages to the glow plug relay? Only thing the ECU should control is the ground that pulls the relay in to close the circuit that supplies 12v and a lot of amps to the glow plugs. As someone else mentioned on the VW TDI you turn the ignition on to activate the glow plugs before you activate the starter. On my JD 870 you turn the ignition switch counterclockwise to activate the intake heater. My Dodge truck you turn the ignition to run to activate the manifold heater. I thought I saw in the diagram that your tractor may also have a manifold heater.

If you did not watch over the field mechanic do you know if he or she did any multimeter testing? Corroded connections could be causing the relay to not work. I had my VW chip tuned years ago. That guy removed the ECU, opened the ECU, desoldered the computer chip, programmed the chip and soldered it back. Later tune from another company tuned from the OBD port. A bit of blah blah blah about I do not recall how the ECU box was split open.

I got a Scag zero turn "Died while mowing." Right go arm switch bypassed, fuse holder cut out and wire nutted, seat switch wire nutted, fuel pump not plugged into wiring harness but using wire nut. Dealer sold me wrong arm switches which took me a while to figure out. Sold me NC switches instead of Normally Open switches. PTO switch did not ohm out the way I liked so it was replaced. Plugged fuel pump into wiring harness. Replaced missing fuse holder and fuse. Proper arm switch installed. Jerry rigged throttle cable so it works properly. Starter circuit works again and engine runs. Horrible sound from mowing deck and crummy quality of cut. Bent deck and a lot of spindles with bad bearings. Driveshaft to gearbox also has bad bearings and destroyed seal journal surfaces. Mower deck cracked. Lots of grease fitting with factory paint on a 16 year old mower. Eventually I will get that deck straight, cracks welded, seal journals welded and turned back to size.

Anyhow if you have time, a multimeter and a helper you could figure out what is missing electrically from the glow plug relay and then trace that back to the ECU wiring plug. If you only had time and some daylight. That ground wire terminal 5 to the relay looks like you only have a few seconds to test on a cold day.

 

[Hay Dude]

Yep, it’s not easy as it seems, and I am not an electronics expert, so I came seeking advice on fixing existing system. Thanks for suggestions

 

[Hay Dude]

Wonder how long the tractor would be down waiting on them to rebuild the ECU?

Or if the ECU isn’t on its way out with other functions?

 

[MossRoad]

I thought of trying that last year, but I ran it by someone who was an electronics tech in the military and he thought it would not be a good idea since the tractors have different programming.

If it was a mechanical part, I'd do it. But electronics... if it blows you now have 2 machines that don't work.

I ran into a lot of this at my last job.... people wanting to swap boards from a good working machine into a bad non-working machine. We only had 2 machines, and they wanted me to possibly make them both dead. No way.

If I had at least a pair and a spare, I'd consider it. But not with just 2 machines.

 

[CalG]

Lots of pages I have not read here, but has it been mentioned that "some" glow/preheat components do not tolerate full 12V battery voltage during the heating process. That is, the multiple heaters (glow plugs) need an additional dropping resister to limit applied voltage to keep from burning out the heater elements. Some do, some do NOT.
The B7200 has a bare wire coil that heats and glows red , visible through a hole in the dash.

Such information and "matching of components" is important when jury rigging any work around.

Wouldn't want to burn out all the heaters and add to the cost of learning.

 

[MossRoad]

Or if the ECU isn’t on its way out with other functions?

Yeah, that's a possibility. But at least you have a plan to get the glow plugs working if it's not the corrosion issue you mentioned. Then only time will tell if other functions of the ECU will go out.

 

[Larry D Johnson]

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?

Take a look at a cheap Chinese tractor. You will find a a spring loaded switch (some are on the keyswitch turn it left for glow plugs). A fuse and wire going to the glow plugs. Simple and it works. Good luck!