JD X749 Dying after 30-45 minutes

[Mike VS]

Hi all, My last post was almost 2 years ago trying to fix this same problem. First the problem, then what I have tried.
This X749 has a 3 cylinder Yanmar with less than 300 hours. It runs and cuts flawlessly and looks like a new motor/mower. It always starts right up regardless of the temperature and has zero issues other than this. When I start cutting the grass all if perfect until 30 to 45 minutes later when it suddenly dies, sometimes as if I had turned the the key off, other times it sputters a little then dies. It will restart immediately but will die 20-30 seconds later. When I let it sit for 5 minutes, it will run for another 15 more minutes. The run times are extended the longer it sits to "cool down". It doesn't matter if it is cutting 2' tall grass or running in neutral at the shop, it's going to die. It doesn't matter if it's 60 degrees or 85 degrees outside.
Now, this whole time the temp gauge does not show hot, as a matter of fact it is between 25% to 33% in the green and has NEVER gotten any where near the red zone. It operates normally up and down. And it is not acting even slightly like it is running hot, it feels very cool and never gives the impression of an overheated motor.
What I have checked: My prior post helpers have suggested cleaning the screens around the radiator, they are spotless. The thermostat was removed and tested; it opens and closes perfectly. The antifreeze was changed; it looked like new from the bottle. The radiator interior looks like a brand new machine, no rust not even discoloration, all perfect. No dirt or junk in or near the oil cooler or radiator, all clean. Fan, belt, and water pump perfect. Fuel filter changed. Fuel cap vent not plugged.
My question is: What shuts down the fuel supply when it does overheat? I see a solenoid attached to the injector pump, is that what's shutting it down? And where does it get it's signal from, the temp gauge sending unit or a separate sensor? Last year I just lived with it after not being able to figure it out, and just sat back and smelled the roses while it cooled down... I'm sick of that smell about now!

 

[Mike VS]

Yes, but I'm not sure how to diagnose it. Since it will restart immediately upon stalling, it will be hard to test voltage when it's dead. I suppose I could rig a voltmeter on the dash and look when it dies. Do you know where overheat sensor is that triggers this to turn off? Is it just the temp sensor?

 

[radios1]

Yes, but I'm not sure how to diagnose it. Since it will restart immediately upon stalling, it will be hard to test voltage when it's dead. I suppose I could rig a voltmeter on the dash and look when it dies. Do you know where overheat sensor is that triggers this to turn off? Is it just the temp sensor?

it wouldn't be a temperature sensor, since it restarts immediately upon stalling. to narrow it down, you can freeze that solenoid with "freeze spray" and if you get another 30 minutes out of it, then you have a bad solenoid.

 

[Mike VS]

it wouldn't be a temperature sensor, since it restarts immediately upon stalling. to narrow it down, you can freeze that solenoid with "freeze spray" and if you get another 30 minutes out of it, then you have a bad solenoid.

That's not a bad idea. I'll get to the store and buy some.
I'd still love to know where it gets it's overheat signal from, it could be bad as well.

 

[Fuddy1952]

That's not a bad idea. I'll get to the store and buy some.
I'd still love to know where it gets it's overheat signal from, it could be bad as well.

You can use dusting spray (inexpensive), hold can upside down for freeze.

 

[wvgca]

My first thought was something is causing a vacumn, but if you have already changed the fuel filter, and are sure that there is a working vent in the gas cap, ll that can be left is the solenoid ... if it's not too expensive, just change it, and go from there ..

 

[Dave M7040]

Please read the description of the Yanmar Engine Stop solenoid I have attached.

Understanding the two internal coils and their respective functions may help diagnose your sudden stopping problem.

My suggestion is to temporarily wire two small lights at the solenoid. There will be a two wire connector at the solenoid and you want to connect a light bulb to each wire and to a ground.

Locate the lights where you can easily watch then. As you crank the engine you should see one light turn on which is the PULL-IN coil and when you release the key switch back to On, the other light bulb, connected to the HOLD coil should light while the first bulb goes out.

As you use the tractor, keep your eye on the HOLD light bulb. If it ever goes out while you are using the tractor, you know the solenoid is stopping the engine and now you can start to find out why.

You can temporarily connect the light bulbs using a Tee connector as shown in this Youtube video.

How to connect wires using t-tap connectors (wire taps) - YouTube

Dave M7040

 

[Mike VS]

Yes, rig up a meter and see if the voltage on the "hold-in" coil drops out when the tractor quits. If it does drop out, then something is telling it to drop out, other than a possible connection problem. However, I feel the the voltage will remain when the tractor dies.

I think you're kind of missing the point on the overheat idea. The solenoid is probably bad because the hold-in coil is going bad. The freeze spray is a good idea to try.

I'll get on testing it tomorrow.

 

[Mike VS]

That is a huge help, thanks Dave. I found the solenoid has 3 wires but I'm sure one (maybe black wire) is ground, the other two are power. I'll be testing tomorrow. Also, I found the solenoid on Ebay for $14.00 delivered (vs. $105 from JD) I'm going to buy it regardless.[/QUOTE]

 

[Mike VS]

Please read the description of the Yanmar Engine Stop solenoid I have attached.

Understanding the two internal coils and their respective functions may help diagnose your sudden stopping problem.

My suggestion is to temporarily wire two small lights at the solenoid. There will be a two wire connector at the solenoid and you want to connect a light bulb to each wire and to a ground.

Locate the lights where you can easily watch then. As you crank the engine you should see one light turn on which is the PULL-IN coil and when you release the key switch back to On, the other light bulb, connected to the HOLD coil should light while the first bulb goes out.

As you use the tractor, keep your eye on the HOLD light bulb. If it ever goes out while you are using the tractor, you know the solenoid is stopping the engine and now you can start to find out why.

You can temporarily connect the light bulbs using a Tee connector as shown in this Youtube video.

How to connect wires using t-tap connectors (wire taps) - YouTube

Dave M7040

Thanks Dave, this is a big help. I will be testing tomorrow but I have found a new one for $14 on Ebay. that's a no brainer, I bought one.

 

[Mike VS]

FAILURE! I bought the new solenoid with total optimism and installed it this morning. All started well, but sure enough 40 minutes later it died. I let it sit 2 minutes and got 5 more of cutting time. After a 10 minute sit I finished the job of 15 minutes cutting.
The temp gauge was at 33% of the green and was again not acting hot. The good news was that I only paid $14 delivered for this so I'm not too pissed. So what's everybody's next idea?

 

[wvgca]

okay, so you're out 14 bucks, not big deal ...
anyways, what else feeds it?? just one sensor or two??

 

[Mike VS]

okay, so you're out 14 bucks, not big deal ...
anyways, what else feeds it?? just one sensor or two??

There are two hot wires going to the solenoid, one gets hot upon startup, the other gets hot when ignition is on while the start up goes cold. I have been advised here to rig light bulbs to those and see if I lose the hold power. I've been too busy to do it hoping this would just solve the problem. I'll rig the bulbs soon but if I do lose power to the hold solenoid, where would that sensor be coming from?

 

[wvgca]

probably from the temp gauge, not sure, you would have to find a wiring diagram ...
you can put in a new temp gauge [especially if it's cheap] or take it right out and put a plug in the hole ...
this will [kinda] simulate a cold engine to the solenoid, maybe it might make a difference ..

 

[Mike VS]

UPDATE> Ok, my test lights are complete and here are the results:
The white solenoid lead is the startup power. It does in fact come on with the starter and then go out. The red lead is the hold, and it also comes on when is running and stays on.
So, I finished cutting the grass this morning and was out of work for "overheat testing" so I started in and sat in my yard watching for the light bulb to go out when the engine died. Sure enough 30 minutes later it died and behold the light stayed lit until turning the ignition switch off. So my take is it's not the shut off solenoid but somewhere else, although if I had not just replaced it I would have suspected it to be bad.

The past poster suggested I remove the temp sender which is a little overkill, maybe I'll remove the sender wire and see if it dies. What possible other sensor could be doing this?

 

[wvgca]

if it's got murphy type switches, they will be on the water temp, and the oil pressure anyways, but the light would have gone out ???
your back to a vacumn forming someplace, try running with the gas cap loose, or change the fuel filter, or both .

 

[Mike VS]

if it's got murphy type switches, they will be on the water temp, and the oil pressure anyways, but the light would have gone out ???
your back to a vacumn forming someplace, try running with the gas cap loose, or change the fuel filter, or both .

Yes, I switched it with my other JD tractor, THEN loosened it while cutting... still died. And I replaced the fuel filter.

 

[radios1]

Yes, I switched it with my other JD tractor, THEN loosened it while cutting... still died. And I replaced the fuel filter.

it's not senders or sensors. the only thing that will stop a diesel is cutting off the air or fuel supply, does it have a lift pump?. that could be bad, if not, then you may have junk in your tank, or fuel lines, don't waste time with senders or sensors, it's the fuel supply!!..

 

[crashz]

Well, you are making progress. You know that the tractor is not shutting itself down due to a sensor or failed hold coil.

The timing thing is weird, but once shut down you have limited use until cooled. Or maybe fuel is restricted?

I know you tried swapping fuel caps, but maybe its not vented through the cap. Maybe the tank vents another way? I would try two things:
- Try running it stationary without any fuel cap. Open top. Or mow for 25 minutes with the cap on, park it idling, and unscrew the cap and leave it off. If it still runs or if you feel a vacuum, you know you have a vent issue.
- Its possible that the tank could have something in it that is blocking the fuel feed hose. If/when it dies again, leave it dead, grab a drain pan and pull a fuel line off of the filter housing.

I doubt this is a pump failure as once they die, they don't typically restart at all.

 

[Mike VS]

Well, you are making progress. You know that the tractor is not shutting itself down due to a sensor or failed hold coil.

The timing thing is weird, but once shut down you have limited use until cooled. Or maybe fuel is restricted?

I know you tried swapping fuel caps, but maybe its not vented through the cap. Maybe the tank vents another way? I would try two things:
- Try running it stationary without any fuel cap. Open top. Or mow for 25 minutes with the cap on, park it idling, and unscrew the cap and leave it off. If it still runs or if you feel a vacuum, you know you have a vent issue.
- Its possible that the tank could have something in it that is blocking the fuel feed hose. If/when it dies again, leave it dead, grab a drain pan and pull a fuel line off of the filter housing.

I doubt this is a pump failure as once they die, they don't typically restart at all.

Thanks... As far as the venting on the cap, I know that is not it. I literally had the cap falling off and it died. With that loose there would be no vacuum. Now a fuel blockage is possible, but due to how well it runs under a full load I just don't see it. There is 100% power under all conditions until it just shuts down. And it doesn't sputter and slow down, it dies like you shut the key off. Hard to believe the fuel supply is coming and going like that.