Snow Non-functioning glow plugs on Grand L's, expecting snow

[design]

Winter is hear, and I just found out that the glow plugs are no longer working. (I am really, REALLY glad I installed the block heater last summer when I did the fluid change !, or the tractor would be a pretty, orange, boat anchor until spring.)
Neither the dash light or the glow plug work. When I look at the electrical schematic it appears that there is a thermistor on the block that goes to a glow plug controller that goes to a glow plug relay.

1. What is the controller looking for? Low resistance or an open circuit?
2. Can I trouble shoot by by passing the thermistor and grounding the white wire leading to the controller?

I am trying to determine if the issue is the wire harness, the thermistor or the glow plug controller.

Anybody try and chase this issue down before?

Design

 

[ozzie tractor]

its not just a blown fuse or something is it?

 

[psdx]

The dash glowplug indicator requires a path to ground in order to light. This path is completed by the glowplugs being screwed into the block. Basically, if you have 12V at the tip of your glowplugs AND the glowplug has not failed, the current loop is completed and the indicator light comes on. A simple first test is to have someone operate the ignition switch to the glowplug preheat position and use a simple volt meter to test for 12V at the glowplug tips.

If you do have 12V, then remove the glowplug and check its resistance. It should be 2-4 ohms. If it's higher than that, replace the glowplug(s).

If you do not have 12V at the tip of the glowplugs, then it's time to work backwards towards the ignition switch. The next thing would be to check for 12V on the output side of the relay (while someone operates the ignition switch to the preheat position). I can't offer any more suggestions without seeing your specific diagram. But these are some starting points. It's a very simple system and shoukd be easy to diagnose and repair. Let us know what you find.

 

[jfay]

I had the same problem on my L3300. It turned out to be a bad controller. Easy to replace. If you search the archives there are a bunch of posts on this.
Good luck.

 

[*kosmo*]

dittos on my L2900. it had a bad glow plug controller (about $62.00). its under the dash and not too bad to get to. good luck!!

ftr.....my glow plugs worked sometimes, and sometimes they didn't.

 

[Kubota3710]

Not sure if the L2900 glow system is similar to the L3710 system. I read through the maintenance manual on how the glow plug system worked in detail.

When the system is working, you turn the key to on and the glow controller checks the temperature, then energizes the glow plug relay, providing 12V power to the glow plugs. The time the glow plug controller energizes the glow plug relay is based on the temperature of the thermistor.


On the L3710, even with a bad glow plug controller and a bad glow plug relay, when you move the key from on to the start/crank position , 12V power is provided directly to the glow plugs(different circuit). So the tractor make crank a bit longer, but with the L3710 when the key is moved from on to CRANK, the glow plugs are getting 12 volts and it should eventually go varoom. When my glow plug controller was bad (no preheat) crank times were 10 seconds. After I replaced the glow plug controller (Preheat working), crank times are back down to a couple seconds. (It ain't that cold in Alabama. )

I'm not sure if Kubota meant it that way, but it is kinda like a fail safe system for starting.

Rich

 

[design]

Thank you.
Crank times at 40 deg F are 10-12 seconds. By moving the wire between the controller and the thermistor, I was able to get the glow plugs to work once. So I am wondering if the issue is the controller, the thermistor, or the wire between them has a short?
The good news, if you leave the block heater on for 3 days, (I just did that by accident) the only bad news is the electric bill ends up being a bit higher but the tractor started very well.

Design

 

[Kubota3710]

You can check the thermistor if you have a multimeter (ohms at spec)
You can check continuty of the wire between the thermistor and glow controller if you have a multimeter. (Resistance near zero)
You can check that 12V power is getting to the glow plug relay and glow controller using the trouble shooting procedures in the maint service manual. (Basically checking to ensure the wiring harnesses are ok)

The bad news is my book says if everything else seems fine but the glow plug system isn't working, replace the glow plug controller. In other words, there doesn't seem to be a test procedure to verify whether the controller is good or bad.

If you read all the associated threads in the forums, the glow plug contoller seems to be the most common failure item in the glow plug system. A new one for my tractor was $65 if I remember correctly. Mine lasted five years and 730 hours before failing.

 

[design]

Great advice on checking with a multi meter. Never though of that.
Thanks alot.
Design