MX5000 randomly stalls

[jcaron2]

My MX5000 has developed an electrical issue lately, and it seems to be getting worse. The tractor will be running normally, when all of a sudden the fuel pump solenoid will begin clicking sporadically, and the engine will spit and sputter and eventually cut off completely. Even after it has stalled the solenoid continues to click randomly. Then, suddenly the problem goes away, and the tractor is back to normal for a while.

I've checked the switches at the seat, PTO, and gear shift, and they all seem fine. Besides, it doesn't seem like it would be one of those switches or else the starter would be affected as well, but it's fine.

I've also jiggled, jostled, and wiggled pretty much every wire connection on the tractor trying to fix the problem when it's happening or trying to reproduce it when it's not, and I've been unable to make any difference that way.

Unfortunately, I don't have a schematic of the electrical system or a parts list for the tractor, so I'm taking educated guesses as to what's going on, but here's what I've observed:

When running normally, the voltage at the fuel pump solenoid is 12V, so that helps me rule out the possibility of a resistive connection somewhere causing the voltage to teeter around some threshold where the solenoid turns on and off.

Unfortunately, I'm never able to reproduce the problem when I have my multimeter handy, so I don't know what the voltage is when the solenoid is clicking, but I'd be willing to bet a fair amount that it's fluctuating between 0 and 12V.

If I trace the wire from the solenoid back toward the front of the tractor, it eventually goes to a relay with four connections. Again, since I can't reproduce the problem until I put away the multimeter, I've been unable to diagnose if that relay is the issue.

Can anyone tell me if this is the OPC timer relay? Given that the OPC system gets inputs from the seat, the PTO, and the gear shift, it doesn't seem like four connections would be enough, so maybe it's another relay (e.g. starter relay)?

Either way, based on a couple of previous threads on this forum, my hunch is that the OPC relay is the source of my troubles, but I thought I'd see if anyone here has an opinion on the matter or some suggestions for further troubleshooting before I buy a new OPC relay.

Josh

 

[collije]

I have not had the exact same situation before but this sounds like a ground issue to me. I would check all of the grounds associated with the solenoid and the main grounds that support the entire machine. Even if the starter and all work fine there could still be a ground issue. I did have the ground issues with lights on some of my cars and trucks which is what leads me to this end.

Good luck, those intermittent things are very hard to find sometimes.

 

[jcaron2]

I have not had the exact same situation before but this sounds like a ground issue to me. I would check all of the grounds associated with the solenoid and the main grounds that support the entire machine. Even if the starter and all work fine there could still be a ground issue. I did have the ground issues with lights on some of my cars and trucks which is what leads me to this end.

Good luck, those intermittent things are very hard to find sometimes.

The solenoid is "self-grounded" so to speak, since it's made largely out of metal and bolts directly onto the engine. The only wire going to it is hot, and the ground return is made through the body of the tractor, so I don't think ground at the solenoid is the problem.

It could be the ground connection at one of the relays, but until I can catch it in the act armed with my multimeter, I won't be able to check.

 

[dougtrr2]

Don't overlook the solenoid because you think it is "self grounded". It could have corrosion underneath. Battery cables are a lead to lead connection at the battery and they can still have bad connections.

Take Care
Doug in SW IA

 

[jcaron2]

I got some clarification on the whole Operator Presence Control (OPC) system. I figured I'd post what I learned here in case somebody has a similar problem in the future. I think a lot of the L-series tractors (and maybe B- and BX- series too?) have the same system.

Fuel delivery to the engine is shut off by default. In order for the engine to run, power is applied to the solenoid, which causes the engine-stop lever to disengage, thereby allowing fuel to flow. As far as I know, this is opposite of the "old" style, where the solenoid had to be engaged in order to shut off fuel flow.

Power to the solenoid is delivered through the Key Stop Solenoid Relay. This is the relay I mentioned in my original post above. It's a very simple SPST relay. A 12V or 0V signal across the coil terminals controls whether a third switched terminal is or is not connected to 12V from the battery at the fourth terminal. Functionally speaking, it's exactly the same as a garden-variety relay like you'd find throughout your car - a control voltage across two terminals controls whether the other two terminals are connected together or not. Kubota, however, is apparently very proud of this particular relay, because they want $129 for a replacement.

The control voltage to the Key Stop Solenoid Relay is supplied by a second relay, called the OPC Timer. The control voltage for the OPC Timer relay is supplied by a circuit combining the various safety switches at the seat, PTO, and gear shift lever. Suffice it to say that the control input on the relay sees 12V when everything is okay, and 0V if something is wrong (e.g. your butt is off the seat while the tractor is in gear and/or the PTO is engaged). The only thing differentiating the OPC Timer relay from a more traditional relay like the Key Stop Solenoid Relay is that it has a built-in ~1-second delay before it switches off. Presumably this is to keep the tractor from cutting out whenever you hit a bump and bounce up off the seat temporarily. Despite the fact that it's more specialized than the previously-mentioned relay, Kubota sells the replacement part for this one for a mere $59.

As I said above, the switched output of the OPC timer relay is the control input to the Key Stop Solenoid Relay. This switched voltage is supplied to the OPC timer via the ACC connection (i.e. it's only got power when the key is in the "ON" or "START" positions). This is as opposed to the Key Stop Solenoid Relay, whose switched voltage is supplied directly by the battery (as I already mentioned above).

I haven't been able to diagnose yet which of these two relays is the problem, but I'm pretty sure it's got to be one of them.

Hopefully this info can help somebody with similar problems in the future.

Josh

 

[jcaron2]

Just an update, I finally got the tractor to "act up" while armed with my multimeter. I verified that as the solenoid clicked in and out, the control voltage on the Key Stop Solenoid Relay did indeed fluctuate between 0V and 12V, indicating that that relay is working just fine and is merely doing as it is told by the control voltage. Thus, the problem has to be "upstream" from that relay, meaning that it's either the OPC timer relay or one or more of the safety switches. As I mentioned above, I don't think it's a safety switch issue because the problem occurs regardless of whether I'm sitting on the seat or not, or regardless of whether or not the gears and/or PTO are engaged.

So I had my dealer order me a new OPC timer relay. Meanwhile, since it won't be here until next week, I went ahead and bypassed it. Wiring the OPC relay output directly to the 12V ACC line would allow the engine to run any time the key is on, but it would also bypass the safety switches. Therefore, instead, I wired the relay's output to its control line input. This effectly just removes the one-second time delay provided by the relay. So until I install the new relay next week, my tractor will stall immediately if I fall off it, rather than one second later like it's supposed to.

 

[jcaron2]

Closing out this thread, my bandaid worked just fine while waiting for the new OPC timer to arrive. For anyone who needs to do this in the future, just cut the four wires to the timer between the wiring harness and the relay itself, and throw away the bad relay. Tie the solid red and solid yellow wires together and cap off the other two with a wire nut or some electrical tape.

The tractor has run fine for a couple of weeks now, ever since I bypassed the OPC timer. The lack of a time delay before the engine cuts out hasn't even been a problem. Nevertheless, I installed the new timer this evening, and it seems to be running perfectly.

 

[Deano]

Great description of the system...glad you found the problem!!

Deano

 

[bob42041]

I read your problem in 2014, it workwd perfectly with crosssing red and yellow, you saved me a ton of money, thank you.

Closing out this thread, my bandaid worked just fine while waiting for the new OPC timer to arrive. For anyone who needs to do this in the future, just cut the four wires to the timer between the wiring harness and the relay itself, and throw away the bad relay. Tie the solid red and solid yellow wires together and cap off the other two with a wire nut or some electrical tape.

The tractor has run fine for a couple of weeks now, ever since I bypassed the OPC timer. The lack of a time delay before the engine cuts out hasn't even been a problem. Nevertheless, I installed the new timer this evening, and it seems to be running perfectly.

 

[jcaron2]

I read your problem in 2014, it workwd perfectly with crosssing red and yellow, you saved me a ton of money, thank you.

I'm glad to be able to help, Bob!! When I posted the final solution, I wasn't sure anybody would ever read it or find it useful. After all the help I've gotten from this forum over the years, it's nice to know I can pay a little of it back. Thanks for letting me know!

Josh