L2250 glow plug issue

[Passinthrutwo]

Hi all, great forum.
A little background, this is the easiest starting engine I have ever had. At least in the summer. Not so in the winter.

After last snow had a hard time starting, temps in 20's not that bad, so decided to dig into glow plugs. I have a shop manual, how hard can it be.
First thing I did was check voltage at glow plug, which the manual says nothing about doing. I only had 7v so tore everything apart and checked by book.

Starter switch checked good, wiring good, glow plugs .8 ohm, spec is .5 which should be good. Not finding anything and in this far, I decided to get new gp from Kubota.

Installed new plugs and still don't think it's right, I have 12.8 v at power wire at GP.
Hook to GP and drops to 8.1 on preheat and 8.7 on start. Battery holding 12.8 steady.
Glow plugs are pulling 28 amps.

I did a few timed 45sec preheats and didn't see or feel anything at the GP indicator nor did I feel any heat from GP tips. Does anyone know if this is normal. I haven't tried starting it yet, as I still have the intake off. Don't see it being any different.

Has anyone ever checked the voltage at the GP or know what it should be.
Even though the switch ohm out good, could I still be losing voltage there.

Thanks Tim

 

[Roadworthy]

The only glow plug research I've done was for NGK. Most of their glow plugs are supposed to be 10.5 volts. The 12.8 volts at the glow plug sounds about right if the glow plug is not connected. That's the open circuit voltage. There is no reference for regulation with glow plug disconnected. Since your glow plugs only see about 8 volts when in use if the resistance really and truly is .8 ohm the current through each plug is about ten amps so your measured 28 amps is about right. However when working properly the glow plug will be quite hot to the touch, not just warm. Your tractor probably uses a glow indicator on the dash. The terminals corrode over time increasing the resistance so you no longer get full current flow to the glow plugs. Try cleaning the terminals or replacing this glow indicator. It will be a few turns of nichrome wire or some such.

 

[Passinthrutwo]

Thank you for the reply Roadworthy.
Electrical is my weakness.
I Had the indicator out and it ohm out good.

I didn't know if that ment anything once there was a load on it or not.
So I should be looking for about 10.5 v at the GP ?
I put in new NGK plugs but I didn't ohm them out.

 

[Russell King]

A few questions about how you tested the glow plugs:
What part did not get hot?
Were the glow plugs installed in the block when you tested them?
If they were not installed did you ground the proper part of the glow plug?

 

[Dave_eng]

Testing glow plugs in the open air is a bad idea.

They need to be connected to a heavy metal mass to not heat too fast and break apart.

If you must test them out of the head, clamp them in a big vice.

Dave

 

[200mph]

If you’re experiencing a 4 volt drop at the GP, it is either by design or there is a wiring issue. Suggest watching any number of videos on YouTube showing how to conduct a “voltage drop test” it is way more useful in finding issues under load.

modern GP turn red hot in under 4 seconds and close to white hot within 7 second when battery voltage is supplied during bench testing. I can’t speak for older systems though. (I actually tested the ones in my L4740-3)

on older systems a resistor was used to reduce GP voltage and they also need to be energized for much longer times. I’m guessing this may have been due to material and design practices at the time where the GP couldn’t be heated so quickly.

On most newer tractors the GP is energized by the ecu for a maximum of 10 seconds and is often much less.

if I owed an older tractor with the glowing resistor indicator, I’d be tempted to remove existing wiring and convert to newer GP and use a 60 amp relay with a fused 10 AWG wiring. Relay would still be triggered by the Key switch. Simply count to 8 and start.

A wiring diagram for your model would be nice to see.

Please consider learning how to do a voltage drop test. Ive found in invaluable in diagnosing power circuits.

good luck.

 

[Passinthrutwo]

If you’re experiencing a 4 volt drop at the GP, it is either by design or there is a wiring issue. Suggest watching any number of videos on YouTube showing how to conduct a “voltage drop test” it is way more useful in finding issues under load.

modern GP turn red hot in under 4 seconds and close to white hot within 7 second when battery voltage is supplied during bench testing. I can’t speak for older systems though. (I actually tested the ones in my L4740-3)

on older systems a resistor was used to reduce GP voltage and they also need to be energized for much longer times. I’m guessing this may have been due to material and design practices at the time where the GP couldn’t be heated so quickly.

On most newer tractors the GP is energized by the ecu for a maximum of 10 seconds and is often much less.

if I owed an older tractor with the glowing resistor indicator, I’d be tempted to remove existing wiring and convert to newer GP and use a 60 amp relay with a fused 10 AWG wiring. Relay would still be triggered by the Key switch. Simply count to 8 and start.

A wiring diagram for your model would be nice to see.

Please consider learning how to do a voltage drop test. Ive found in invaluable in diagnosing power circuits.

good luck.

 

[Passinthrutwo]

Thanks for all the replies. The only way I tested the GP was with ohm meter. Both installed and out and got .8 ohm both ways.

I figured they were good but decided to put new ones in since I was this far. Never tested them with voltage out of tractor.
New one's in, on preheat for 45 sec. Touching the plugs by hand all over them, no heat at all.

200mph
Yes I am experiencing a voltage drop which I don't think should be there. I will look up the voltage drop test you suggested.
Thank you all

 

[Passinthrutwo]

Ok I read up on voltage drop test ( thanks 200mph ) definitely a good thing to learn.

So did some testing today.
When I turn key to preheat only have 10.6 v
At key switch. Same 10.6 going into GP indicator and 9.6 coming out of GPI.
I heard the GPI is also a resister so loosing
1v there might be right?
And back down to 8v at the plugs

So I suppose first thing to do is get a new key switch.
If I can figure out how I will post the starter
System diagram.

 

[whitetiger]

Ok I read up on voltage drop test ( thanks 200mph ) definitely a good thing to learn.

So did some testing today.
When I turn key to preheat only have 10.6 v
At key switch. Same 10.6 going into GP indicator and 9.6 coming out of GPI.
I heard the GPI is also a resister so loosing
1v there might be right?
And back down to 8v at the plugs

So I suppose first thing to do is get a new key switch.
If I can figure out how I will post the starter
System diagram.

Did you check the voltage at the battery and from the batty cable post on the starter and frame? You may only be getting 10.6 V to the switch.

 

[Passinthrutwo]

Did you check the voltage at the battery and from the batty cable post on the starter and frame? You may only be getting 10.6 V to the switch.

Yes I got 12.8v at both.
When preheating the batt drops to 12.5 or so.
I did not check voltage at starter under load

 

[Dave_eng]

I am going to take a long shot here and suggest your glow plugs are designed to be wired in series and not parallel and this mis-wiring is why things are not working properly and you cannot measure the right resistances.

I suggest this after looking at the L2250 wiring diagram which is below.

I draw your attention to the one electrical ground symbol in the GP wiring.

Contrast the above wiring depiction with a more common parallel wiring setup as shown below where each GP is shown with an individual ground provided by the cylinder head itself.

Series wired glow plugs are completely different than the more common parallel ones in terms of internal structure and also how they are wired.

I suggest you start by posting a photo of the glow plug side of your engine. Also provide the part number of the GP's you bought.

Dave

 

[Russell King]

Yes I got 12.8v at both.
When preheating the batt drops to 12.5 or so.
I did not check voltage at starter under load

Whitetiger was wanting you to verify the voltage between the battery cable on the starter to a frame ground (to verify the battery negative is connected to the frame well). Not sure if you need it under load at all, but if you’re able to provide voltage before trying to cranK engine and also while cranking then that would help eliminate the concerns of the wiring to battery.

 

[North Idaho Wolfman]

I am going to take a long shot here and suggest your glow plugs are designed to be wired in series and not parallel and this mis-wiring is why things are not working properly and you cannot measure the right resistances.

I suggest this after looking at the L2250 wiring diagram which is below.

I draw your attention to the one electrical ground symbol in the GP wiring.

View attachment 53330


Contrast the above wiring depiction with a more common parallel wiring setup as shown below where each GP is shown with an individual ground provided by the cylinder head itself.

View attachment 53333

Series wired glow plugs are completely different than the more common parallel ones in terms of internal structure and also how they are wired.

I suggest you start by posting a photo of the glow plug side of your engine. Also provide the part number of the GP's you bought.

Dave

Dave,
That wiring schematic is somewhat misleading, as All Kubota's use parallel wired glow plugs as they all have grounds on the body of the glow plus thus they share the same grounds.

 

[Dave_eng]

Dave,
That wiring schematic is somewhat misleading, as All Kubota's use parallel wired glow plugs as they all have grounds on the body of the glow plus thus they share the same grounds.

NIW

Not wanting to argue but there are some L's that are series. L210 being one of these.

The series wired ones have a ground wire from the last GP to the block as you see in the yellow text marked one in this photo.

This page from the shop manual clearly states the L210 is series while others of similar age are parallel.

The GP's for series wiring actually have two separate electrical connections at the top of the GP.

Some early B's were series wired and had a large resistor in a metal can in front of the steering box.

I agree that Kubota series GP's are unusual but in my experience they have existed in a few models of older Kubota's for reason's I never understood. Perhaps these are engines Kubota bought from another manufacturer. In these specific instances their wiring diagrams are different than the normal Kubota parallel wired GP's.

You are likely right that in the case of the L2250 the wiring diagram is misleading but I wanted to raise it as a possibility because of the wiring illustration.

Dave

 

[North Idaho Wolfman]

NIW

Not wanting to argue but there are some L's that are series. L210 being one of these.

The series wired ones have a ground wire from the last GP to the block as you see in the yellow text marked one in this photo.

Dave

You are 100% right I forgot about the very early Kubota's did use series Glow Plugs.

I would have been better to state that the L in question does not use series plugs they use parallel wired plugs with only one wire connection, the block is the other connection.

 

[Dave_eng]

You are 100% right I forgot about the very early Kubota's did use series Glow Plugs.

I would have been better to state that the L in question does not use series plugs they use parallel wired plugs with only one wire connection, the block is the other connection.

Glad we agree on the old ones............ as an old guy it makes me feel better

Dave

 

[Passinthrutwo]

Thanks for all the replies.
Did some more testing, load tested pos.term. To starter and neg. Term to ground and both showed very low readings. Tested the v going into switch and was only 10v. I think I must have a problem from the starter to switch. Next step tear in wiring harness. Will keep you updated.

 

[John Arthur]

I have this problem. I know the glow plugs are in series. Is the indicator in series with the glow plugs or parallel to the glow plug circuit? My indicator is burnt out and Kubota no longer makes it. Do I need the indicator in working condition for the plugs to heat? If not, how long in seconds do I energize the plugs to get them hot?

 

[John Arthur]

Glad we agree on the old ones............ as an old guy it makes me feel better

Dave

Hi Dave, one old guy to another-great answer. I posted a related question about this problem. Please help this old guy out. Does the glow plug indicator need to be operational for the glow plugs to heat? Mine’s burnt out and it’s a discontinued part.