L3010 HST Wont start, I'm puzzled

[DSH]

I recently bought a used L3010 HST with 1,000+ hours. Been doing some much needed maintenance. Went to start it & get normal dash lights, but won't turn over. Started to try & diagnose the problem & I am coming up with more questions than answers. I assumed it was a safety switch so I started checking. Here's what I have found so far.

- PTO switch has been bypassed
- HST pedal switch has been bypassed
- clutch switch seems to operate properly
- I get 0 ohm between the safety switch leg to the start relay and ground. After a few seconds it climbs to .5 ohm
- Start relay checks out ok
- Ignition switch checks out ok
- Battery voltage is 12.7
- When turning the ignition switch to start, the voltage on the B terminal immediately drops from 12.7 to 11.3
- With ignition switch on start I get 11.3 volts across the two control terminals on the start relay

Why is the voltage dropping when the ignition switch is at start? It's not the load of the starter since it happens when I test with the start relay out, so the starter is not getting activated. It's been a long time since I diagnosed anything on a tractor & apparently I am very rusty.

Other info: New battery made no difference. Battery ground cable was very worn & I replaced it. Positive battery cable clamp was cracked & I replaced it with a clamp on end. It feels cheap, but seems solid for the time being. Tractor has a mid PTO but I don't see any safety switch & I don't see one shown on the schematic. The tractor seat has a safety switch, but there is no wiring to it and I don't see a seat safety shown on the schematic.

What am I missing here? I have spent a few hours trying to figure this out & I am getting humbled. It is probably something simple I am overlooking but I could sure use some input here.

Thanks in advance for any guidance!

 

[Pawnee]

You say the start relay checks out Ok.
So, when the relay is closed do you get voltage at the starter motor?

You replaced the positive battery connector.
If you measure between the battery post and the positive cable you should get ~zero volts with the ignition switch on start. Anything more means you have to make a better connection.

Did it ever start?

 

[Russell King]

The glow plugs are most likely being powered when the key is in the start position.

The glow plugs are usually powered in two key switch positions, warm glow plugs and the start position both supply power to the glow plugs. Usually through a voltage drop resistor in glow position and the starter will drop voltage when key is in the start position (assuming the starter is functional)

 

[Henro]

So the starter is not turning when it should.

If it were me I would determine whether the starter is the problem or something else. There should be a wire on the starter that activates the solenoid, and when energized the solenoid causes the starter to turn. You need to find that wire terminal on the starter motor and see if it’s getting the proper 12 V.

You could put a jumper between the 12 V heavy conductor wire that goes to the starter, and the terminal that is energized when the starter solenoid is supposed to activate. If you would do this you need to be very careful and make sure the tractor is in neutral and cannot move if the engine starts.

If the starter motor main wire has 12 V on it, and putting 12 V on the starter solenoid terminal does not cause the starter to turn over, I suppose you could still have a problem with the ground wire between the engine and the frame. But one step at a time…

If you would try the above and the engine started, then you would know the issue is in the safety circuit feeding the starter solenoid terminal. If not, check you connection between the engine and frame.

edit: I don’t know your tractor but some Kabota tractors have the starter solenoid circuit completed through a fuel cut off solenoid coil. This could be another possible issue but one step at a time…

 

[DSH]

Thanks all for the responses.

Pawnee: The start relay is not closing. Apparently 11.3 volts is not enough to pull it in. I tested it with a 12+ volt supply & it did close. If I jumper the load side contacts at the relay the starter comes on strong. I just did a quick check across the battery post and the + cable close to the battery & got 0 +/- volts.

Russell: I have waited until the glow plug light goes out (only 1-2 seconds) before moving to start. I am assuming that the glow plugs are not drawing current if the indicator on the dash is off. Maybe a bad assumption?

Henro: The starter & solenoid look to be ok. The starter relay is just not closing with 11.3 volts.
Per the schematic, the safety circuit just brings the ground side to the start relay. I checked resistance from the safety circuit connection at the relay to ground and got 0 ohm. Doesn''t that tell me there is good continuity through the safeties?

 

[Dave_eng]

Thanks all for the responses.

Pawnee: The start relay is not closing. Apparently 11.3 volts is not enough to pull it in. I tested it with a 12+ volt supply & it did close. If I jumper the load side contacts at the relay the starter comes on strong. I just did a quick check across the battery post and the + cable close to the battery & got 0 +/- volts.

Russell: I have waited until the glow plug light goes out (only 1-2 seconds) before moving to start. I am assuming that the glow plugs are not drawing current if the indicator on the dash is off. Maybe a bad assumption?

Henro: The starter & solenoid look to be ok. The starter relay is just not closing with 11.3 volts.
Per the schematic, the safety circuit just brings the ground side to the start relay. I checked resistance from the safety circuit connection at the relay to ground and got 0 ohm. Doesn''t that tell me there is good continuity through the safeties?

You are not understanding Russell's description of the GP operation. Read his post again!

Dave

 

[Russell King]

I think that you are correct that the glow plugs stop drawing power when the indicator light goes off but I think they will draw power in the start position with no indicator light on. I think the indicator circuit is bypassed when key is in the start position but the glow plugs still are fed power.

But I don’t have a schematic to review. I am only stating what I know about Kubota glow plug operation on my L185 and several schematics I have seen on other Kubota models. I also know that engineers like to keep systems similar over time if that system has proven to be successful over time.

 

[Mark_BX25D]

The starter relay is just not closing with 11.3 volts.

That should be plenty. Something ain't right here.

I checked resistance from the safety circuit connection at the relay to ground and got 0 ohm. Doesn''t that tell me there is good continuity through the safeties?

Do you have the battery disconnected when testing continuity? If not, your readings may not be valid.

 

[Pawnee]

I'm with Mark, the starter relay should operate on far less than 12 volts.
If a new one isn't too dear I'd replace it and go from there.
If they want way too much I'd take it apart, there might be a miniature mouse nest in it.

 

[Dave_eng]

I have attached 4 pages from the WSM dealing with investigating the starting system.

Also below the schematic and operational description of the GP's

Note on this tractor the glow relay's main function is turning on the Glow lamp during pre heating otherwise in the START position the key switch send power directly to the GP's without using the relay.


Dave

 

[DSH]

Mystery solved (probably). Tested the start relay again with a 12.5+ V battery. This time instead of a loud snap & closed contacts I got a very quiet click & the contacts stayed open. Time to send some more $ to Messick's.

Thanks all for your help on this.

Russell: Thanks for the lesson on glow plug operation. It never occurred to me that the glow plugs would be activated even if the temperature isn't calling for much preheat. Guess that explains the voltage drop when the key is at start.

Dave: Thanks much for taking the time to lookup & post the pages from the WSM, and even highlight the part I was missing!

This forum is great. Some very knowledgeable & helpful members. I have a number of other repair projects with this tractor. Hopefully I will just report how well the repairs went, but will probably be back asking for more help.

Thanks again. I'll report back when the new relay arrives.

Dennis

 

[Dave_eng]

Mystery solved (probably). Tested the start relay again with a 12.5+ V battery. This time instead of a loud snap & closed contacts I got a very quiet click & the contacts stayed open. Time to send some more $ to Messick's.

Thanks all for your help on this.

Russell: Thanks for the lesson on glow plug operation. It never occurred to me that the glow plugs would be activated even if the temperature isn't calling for much preheat. Guess that explains the voltage drop when the key is at start.

Dave: Thanks much for taking the time to lookup & post the pages from the WSM, and even highlight the part I was missing!

This forum is great. Some very knowledgeable & helpful members. I have a number of other repair projects with this tractor. Hopefully I will just report how well the repairs went, but will probably be back asking for more help.

Thanks again. I'll report back when the new relay arrives.

Dennis

Dennis
When you report back it helps everyone learn as it completes the loop of questions which, at the time of posting, represent everyone's most knowledgeable guess but not the real answer.

Dave

 

[lugbolt]

On those tractors the glow plugs should be activated when you first turn the key to "on" (run) position, and then should shut off pretty quickly. It is dependent on heat. There is a temp sensor up by the thermostat that tells the glow controller how hot the engine temp is. If it's cold, up to about 15 seconds. If it's warm, as little as one second. The glow controllers are known to fail on these, as are glow relays. Typical complaint is usually glow plug lamp stays on after starting the engine, or occasionally it just won't start when cold (no current flowing to glow plugs).

Russel is right, also when cranking the glow plugs should be activated.

When the glow plugs are active your battery voltage is going to drop off. They pull a lot of juice.

 

[DSH]

Quick update, the starter relay arrived. I plugged it in & the tractor fired right up. As a bonus, this one had a bracket on it so I could mount it with the wires at the bottom. It had previously been hanging from the wires. That may be why it died. If any water got in the area and on the wires it would fill up the relay with water.

Now on to get the headlights & blinkers/hazards working, sheared loader bolts out, bypassed safety switches working, paint & body, .....

Thanks all for the input on this one!

Dennis

 

[Mark_BX25D]

When the glow plugs are active your battery voltage is going to drop off. They pull a lot of juice.

Based on what I know from other vehicles, I'd guess about 7 amps each. I know my truck draws 10 amps each on its AC60Gs. These Kubota GPS are smaller, so maybe 7 amps, possibly 5. So that's 15-20 amps or so for all three.