Glow plugs

[PoTreeBoy]

Prior to replacing this device I was getting no voltage to the glow plugs when the combination was in the preheat position.
I had to turn the machine of manually at the shut off solenoid before this replacement too.

On the schematic it's called a Combination Box, on the parts diagram it's called a Controller. It seems to contain the preheat indicator timer, a starter relay and the circuitry for the start interlocks, and fuel solenoid relay.

I can imagine that troubleshooting and working on one of these ZT's is extremely frustrating. It is very puzzling that you're apparently getting voltage to the glow plug area, but no heat. Also, your statement that the glow plugs weren't getting power until you changed controllers. According to the schematic, the controller wouldn't prevent that. However, it wouldn't be the first time a Kubota schematic was wrong or altered (my L35 schematic didn't show some hazard/turn signal changes that were made on later models).

In any case, I would disassemble that wire and bus bar assembly on the glow plugs, clean the connections and put it back together.

Good luck.

 

[William1]

On the schematic it's called a Combination Box, on the parts diagram it's called a Controller. It seems to contain the preheat indicator timer, a starter relay and the circuitry for the start interlocks, and fuel solenoid relay.

I can imagine that troubleshooting and working on one of these ZT's is extremely frustrating. It is very puzzling that you're apparently getting voltage to the glow plug area, but no heat. Also, your statement that the glow plugs weren't getting power until you changed controllers. According to the schematic, the controller wouldn't prevent that. However, it wouldn't be the first time a Kubota schematic was wrong or altered (my L35 schematic didn't show some hazard/turn signal changes that were made on later models).

In any case, I would disassemble that wire and bus bar assembly on the glow plugs, clean the connections and put it back together.

Good luck.

In my own case, I had voltage to the bus bar but no amperage BECAUSE the power lead was not tight. A real 'Dooh'!!! when I discovered it, I was thinking 'Unbeleiveable!!!' I only discovered it by chance when I started to disassemble to test (ohm out) each glow plug.

 

[Runs With Scissors]

Sorry for the repeats. This forum format is messy with all the ad pop ups. Very annoying.

I agree........except for this ad....I'm ok with this one

 

[GreensvilleJay]

I haven't got ANY ads since I installed the free adblocker plus years ago...

from the schematic you should have hot glowplugs and light when the key's put to 'preheat', cold/no light when key to off or run.
the 'box' doesn't control the glowplugs..it'd need a 50A relay for that.

 

[85Hokie]

I agree........except for this ad....I'm ok with this one

View attachment 118066

You need an adblock in your system!!! I havent seen an ad in 10 years!!!

 

[Weedman]

On the schematic it's called a Combination Box, on the parts diagram it's called a Controller. It seems to contain the preheat indicator timer, a starter relay and the circuitry for the start interlocks, and fuel solenoid relay.

I can imagine that troubleshooting and working on one of these ZT's is extremely frustrating. It is very puzzling that you're apparently getting voltage to the glow plug area, but no heat. Also, your statement that the glow plugs weren't getting power until you changed controllers. According to the schematic, the controller wouldn't prevent that. However, it wouldn't be the first time a Kubota schematic was wrong or altered (my L35 schematic didn't show some hazard/turn signal changes that were made on later models).

In any case, I would disassemble that wire and bus bar assembly on the glow plugs, clean the connections and put it back together.

Good luck.

I traced the glow plug wire and it does split off and go into the controller/ combination box

 

[Weedman]

I traced the glow plug wire and it does split off and go into the controller/ combination box

I think k I need to step away from the machine for a few days and come at it with fresh brain and eyes.

 

[GreensvilleJay]

That wire is a 'signal' TO the control box,why I don't know but for sure the 'control box' ,combination box does NOT power the glowplugs.

Yes, a 'breakaway' can be a good thing unless you NEED the machine up and running...

 

[Weedman]

That wire is a 'signal' TO the control box,why I don't know but for sure the 'control box' ,combination box does NOT power the glowplugs.

Yes, a 'breakaway' can be a good thing unless you NEED the machine up and running...

Does that wire return signal to the glow indicator light to shut off when the plugs are hot enough?

 

[PoTreeBoy]

Does that wire return signal to the glow indicator light to shut off when the plugs are hot enough?

Of course, the controller is a 'black box' to us, but I suspect that (purple?) wire you mentioned is, as GreensvilleJay wrote, a signal that 'tells' the timer that the glow plugs are running. Then, when the timer times out, it opens the (brown w/red stripe?) wire coming from the ground side of the indicator, turning the light off.

Edited to add wire colors shown on schematic as I read them.

 

[Weedman]

Of course, the controller is a 'black box' to us, but I suspect that (purple?) wire you mentioned is, as GreensvilleJay wrote, a signal that 'tells' the timer that the glow plugs are running. Then, when the timer times out, it opens the (brown w/red stripe?) wire coming from the ground side of the indicator, turning the light off.

Edited to add wire colors shown on schematic as I read them.

I'm at a loss. I just don't understand how I can get a reading at all the plugs when the ignition switch is on heat plugs and yet the indicator light won't go off and I can't get it to start. Yet when I bypass the ignition to heat yhe hlow plugs, everything functions normally including the indicator light???

 

[Weedman]

I'm at a loss. I just don't understand how I can get a reading at all the plugs when the ignition switch is on heat plugs and yet the indicator light won't go off and I can't get it to start. Yet when I bypass the ignition to heat yhe hlow plugs, everything functions normally including the indicator light???

Must be some part I've overlooked

 

[PoTreeBoy]

I'm at a loss. I just don't understand how I can get a reading at all the plugs when the ignition switch is on heat plugs and yet the indicator light won't go off and I can't get it to start. Yet when I bypass the ignition to heat yhe hlow plugs, everything functions normally including the indicator light???

I'm usually pretty good at troubleshooting, but sometimes it's only after the problem is fixed that I see the original cause. It could be backfeeding when you power the glow plug bus, don't know. I'd be checking for a loose or broken wire, possibly. Did you clean that bus and wire?

 

[Weedman]

I'm usually pretty good at troubleshooting, but sometimes it's only after the problem is fixed that I see the original cause. It could be backfeeding when you power the glow plug bus, don't know. I'd be checking for a loose or broken wire, possibly. Did you clean that bus and wire?

Clean as a whistle. If the wire was bad why would I get a reading at the glow plugs when it's in preheat?

 

[GreensvilleJay]

Why. ? ..'skin effect', the voltage can be measured on the outside surface of the wire( bundle of smaller wires( strands)) but CURRENT has to flow through the all of the strands. A voltmeter like a DVM or DMM only needs microamps to register the voltage,If the wire is corroded( , greeny-blue-blk) in the inside 'core', it will not pass much current, in this case about 10 amps per glowplug so 30 amps.

It's also possible that the ign switch is defective and not allowing the full current of 30 amps to the glowplugs.

Since you can heat and start when bypassing the switch with a heavy wire from battery +ve to glowplug 'strap, odds are the switch is defective or the wire from it to the 'strap'

 

[Weedman]

Why. ? ..'skin effect', the voltage can be measured on the outside surface of the wire( bundle of smaller wires( strands)) but CURRENT has to flow through the all of the strands. A voltmeter like a DVM or DMM only needs microamps to register the voltage,If the wire is corroded( , greeny-blue-blk) in the inside 'core', it will not pass much current, in this case about 10 amps per glowplug so 30 amps.

It's also possible that the ign switch is defective and not allowing the full current of 30 amps to the glowplugs.

Since you can heat and start when bypassing the switch with a heavy wire from battery +ve to glowplug 'strap, odds are the switch is defective or the wire from it to the 'strap'

I'm not an expert in this area which is why I ask "why?". I will figure out how to test for amperage and go from there. Your input was helpful. Thank you.

 

[GreensvilleJay]

amps is easy.
remove the wire attached to the strip that connects to all 3 glowplugs.
connect an ammeter terminal to the wire, and the other to the 'strip'.
you'll need a DC ammeter good for 40 amps. An old style 'charge/discharge' automotive gauge will be fine,say 60-0-60. Each glowplug take a nominal 10 amps each, so 3 will take 30 amps.

it is unlikely that a DMM will have a 40 DC amp range,so 'old skool' meter will work fine.

 

[Weedman]

amps is easy.
remove the wire attached to the strip that connects to all 3 glowplugs.
connect an ammeter terminal to the wire, and the other to the 'strip'.
you'll need a DC ammeter good for 40 amps. An old style 'charge/discharge' automotive gauge will be fine,say 60-0-60. Each glowplug take a nominal 10 amps each, so 3 will take 30 amps.

it is unlikely that a DMM will have a 40 DC amp range,so 'old skool' meter will work fine.

Shouldn't something else be getting very hot if the amperage isn't going to the plugs?
I feel like wires should be melting or something?

 

[GreensvilleJay]

No. If the glow plugs are NOT drawing power, then current isn't flowing, so no heat is generated.
Any 'open' circuit doesn't consume power. Think of a wall receptacle. You can measure 120 volts AC on it BUT until a load, like a light bulb, is connected, no current flows, so no heat can be generated.
There is a huge difference between 'voltage' and 'current',something I capitalized on 3 decades ago to make a hacker proof communications network.

 

[Weedman]

No. If the glow plugs are NOT drawing power, then current isn't flowing, so no heat is generated.
Any 'open' circuit doesn't consume power. Think of a wall receptacle. You can measure 120 volts AC on it BUT until a load, like a light bulb, is connected, no current flows, so no heat can be generated.
There is a huge difference between 'voltage' and 'current',something I capitalized on 3 decades ago to make a hacker proof communications network.

If I remove a glow plug and connect the wire from the ignition directly to it then it should get hot if the wire and ignition are working properly. Correct?