intermittent electrical problem

[VashonFarmer]

Hey all,

I hesitated to start a new thread, but all the other stuff I have read through does not quite seem to match my problem, so here goes...

This is on a CT225: After running for a short time, the tach stops working. All the other gauges work, including the hour meter, and the tractor continues to run fine. But if I shut it off I can't restart. If I wait a little while, it generally fixes itself. When it is in the no start condition and I turn the key I get a click from the ignition relay, but that's it. The glow plug timer does not start (dash light) and there is no click from the fuel solenoid. There is nothing at all if I turn the key to Start. If I turn the key to the manual glow plug position, the glow plugs heat as normal.

Here's what I have done so far: Meticulously cleaned every ground contact I can find starting with the main chassis ground from the battery. Both battery cables are less than a year old and in good shape. I have checked all the safety switches. I have replaced all the blade fuses in the block. I have replaced the following relays; ignition, pull coil (BTW, what does that one do?) and starter. I have checked the harness plugs under the dash and the plug to the Operation Control Unit. I confirmed that the RPM sender is not the issue: if I pull the plug on that, the tractor starts fine but without the tach.

I've been at this a while and there might be a couple other things I have tried that I'm forgetting right now. I'm starting to think about the OCU itself, but that seems a bit drastic to just replace and hope. It seems like something is being heat effected. Let it cool and I'm good to go.

Any ideas?

TIA

 

[Wagtail]

Well, the key thing that I 'took away' from your described symptoms is that it is a 'heat' problem... something is heating up and, when shut down, will not 'work' until it has cooled sufficiently.

Thermistor of some sort?

 

[radios1]

it does seem like the Operation Control Unit fails after a while, here's a clue. "I confirmed that the RPM sender is not the issue: if I pull the plug on that, the tractor starts fine but without the tach."

 

[VashonFarmer]

Well, the key thing that I 'took away' from your described symptoms is that it is a 'heat' problem... something is heating up and, when shut down, will not 'work' until it has cooled sufficiently.

Thermistor of some sort?

I'm just not sure where the heat might be from. As in engine heat or electrical heat in a wire somewhere. I kind of think it's the second one.

 

[VashonFarmer]

it does seem like the Operation Control Unit fails after a while, here's a clue. "I confirmed that the RPM sender is not the issue: if I pull the plug on that, the tractor starts fine but without the tach."

I think I read in another post somewhere that the tach signal really only goes one other place than the gauge, and that would be the OCU. Is that what you're getting at? Might make sense.

 

[Wagtail]

I'm just not sure where the heat might be from. As in engine heat or electrical heat in a wire somewhere. I kind of think it's the second one.

Or 'electrical' heat within a component... such as the OCU that radios1 suggests.

A relay could act like this too.

 

[radios1]

I think I read in another post somewhere that the tach signal really only goes one other place than the gauge, and that would be the OCU. Is that what you're getting at? Might make sense.

yes, that's what I'm suggesting.

 

[VashonFarmer]

yes, that's what I'm suggesting.

Right. I had thought about the OCU early but was really hoping someone would chime in with a part I had overlooked that might cost something less than the $400 plus they're going to get for that.

Oh well, you can't always win.

 

[ndbobcat]

Right. I had thought about the OCU early but was really hoping someone would chime in with a part I had overlooked that might cost something less than the $400 plus they're going to get for that.

Oh well, you can't always win.

It sounds to me like a problem with the relay. I had a similar issue, tach wouldn't work, lights, and horn too if I remember right. Investigated wiring diagram and identified a relay under the steering wheel. I removed and replaced that relay and the problems went away. You can take a relay from under the hood (hi/low lights I think) and use as a replacement to test if the problem goes away.

Reference this thread here also...

https://www.tractorbynet.com/forums/bobcat-tractors/220165-tach-electrical-issue.html

 

[Bluegrass2621]

I have a CT445. The only issues I have ever had have been electrical, one which included the tach and lights not working intermittently. The fix was a relay out on the firewall in my case.