JD X749 Dying after 30-45 minutes

[Mike VS]

"I have the service manual. I'm trying to attach the wiring diagram pdf"


THANK YOU Andy! That is fantastic.

 

[Diggin It]

Doesn't call out wire colors though so tracing could be an issue.

Also note that it's for a 748 if that matters.

 

[ruffdog]

Doesn't call out wire colors though so tracing could be an issue.

Also note that it's for a 748 if that matters.

The X7** series tractors ran 2 different diesel engines. The older version was a 1116cc size and the newer 904cc size. Who knows if the electrics are the same with the different engines. The different models were for combinations of 2wd, 4wd, AWS.

 

[Mike VS]

The X7** series tractors ran 2 different diesel engines. The older version was a 1116cc size and the newer 904cc size. Who knows if the electrics are the same with the different engines. The different models were for combinations of 2wd, 4wd, AWS.

You had me curious to see what engine I had... Turned out to be the bigger one. I wonder if there was much of a performance increase with the increased displacement.
My game plan in a few days when the grass is ready, is to run it with the existing relay that I removed and cleaned. If it dies again I'll switch the two relays with each other and see what that does. If it still dies after that, I think buying a new relay is a waste. What do you think?

 

[ruffdog]

You had me curious to see what engine I had... Turned out to be the bigger one. I wonder if there was much of a performance increase with the increased displacement.
My game plan in a few days when the grass is ready, is to run it with the existing relay that I removed and cleaned. If it dies again I'll switch the two relays with each other and see what that does. If it still dies after that, I think buying a new relay is a waste. What do you think?

My x744 and dad's x749 are both the larger engines too. BTW...the big engine weighs about 80lbs more too. If it still dies, yes, I would buy a relay and try it as they are not that expensive.

 

[jonsstihl]

glad to here you are starting to see the light at the end of the tunnel. I hope that solves the problem.

 

[Mike VS]

glad to here you are starting to see the light at the end of the tunnel. I hope that solves the problem.

I don't see light, only a deep dark hole!
Today was grass day with high expectations. I started by swapping the two identical relays hoping this would stop the dying. It lasted 66 minutes before it looked at me and gave me the middle finger. I then tried disconnecting the temp sender wire from the thermostat housing just hoping something was getting a false signal... still died. At this point I'm back to a temporary fuel tank and doing that test.
I asked a question earlier but didn't get an answer; Is there a diagnostic test port on these like cars have? I would bring it to JD in a second if they could do a history diagnosis.

 

[deezler]

Ok so let me think this through out loud here: Y'all are saying that since the fuel shutoff solenoid was verified to retain voltage (test light on) during a shut down, that this cannot be the problem. But what else can kill a diesel engine? Its not just fuel flow through the solenoid - you need fuel to actually be injected into the cylinder, at the right crank angle timing, every other revolution. I presume on a small diesel engine like these yanmars, the timing is handled within the injection pump, and the injector for each cylinder simply opens when it is blasted with enough pressure from the pump, right?

How does the injection pump know the right timing to send fuel to each cylinder - is there an electronic crank position sensor? These can sometimes fail when they get too hot. If there is, and the part is cheap, try replacing. Because if the injection pump doesnt know when to deliver fuel to each cylinder... it wont. Even if the shutoff solenoid stays on, you know? If the pump timing is purely mechanical... disregard this notion.

You could also add a cheap, clear fuel filter housing up right in front of the injection pump. Watch this when your engine stalls - is it still full, or does it empty out? This would help verify where int he system the fuel has stopped flowing.

While it has nothing to do with it, my gas JD GT275 also does this. Shuts down when it gets too hot, and loses spark. Have to give it 15 mins to cool down and not try to mow much more. I replaced the ignition coil twice, then put it back to the original coil, and now it's better? very confusing.

 

[Mike VS]

Ok so let me think this through out loud here: Y'all are saying that since the fuel shutoff solenoid was verified to retain voltage (test light on) during a shut down, that this cannot be the problem. But what else can kill a diesel engine? Its not just fuel flow through the solenoid - you need fuel to actually be injected into the cylinder, at the right crank angle timing, every other revolution. I presume on a small diesel engine like these yanmars, the timing is handled within the injection pump, and the injector for each cylinder simply opens when it is blasted with enough pressure from the pump, right?

How does the injection pump know the right timing to send fuel to each cylinder - is there an electronic crank position sensor? These can sometimes fail when they get too hot. If there is, and the part is cheap, try replacing. Because if the injection pump doesnt know when to deliver fuel to each cylinder... it wont. Even if the shutoff solenoid stays on, you know? If the pump timing is purely mechanical... disregard this notion.

You could also add a cheap, clear fuel filter housing up right in front of the injection pump. Watch this when your engine stalls - is it still full, or does it empty out? This would help verify where int he system the fuel has stopped flowing.

While it has nothing to do with it, my gas JD GT275 also does this. Shuts down when it gets too hot, and loses spark. Have to give it 15 mins to cool down and not try to mow much more. I replaced the ignition coil twice, then put it back to the original coil, and now it's better? very confusing.

First, I'm not sure how it gets its fuel timing signal. I assumed it is mechanical.
Next, my fuel filter housing is clear and as its been discussed here, the housing is full to the brim with fuel every time it dies. The fuel pump has also been totally opened up and is clean without obvious problems. The fuel also flows from the tank with rapid gravity flow.

 

[AndyMA]

Here the entire electrical section with wire color codes and troubleshooting in 2 parts as it's too big for one. The X749 & X749 are the same serviceView attachment Deere X748 749 Electrical Part 2.pdf manual

Andy