JD X749 Dying after 30-45 minutes

[Mike VS]

Again form memory, the shut off solenoid should be a three wire. One ground, one pull in circuit(high current) and one hold in circuit (lower current). Used to be red,black and white. The pull in coil activates with the key switch once the parameters are met and pulls the pin in on the solenoid letting the plunger in the injection pump move back due to spring pressure.
There is a timer circuit that shuts off the relay for the pull in coil after a few seconds. The hold in circuit should be activated and holding in the solenoid via a relay on the third wire. (Low current draw)This will stay held in until the key is cutoff,a safety switch/engine protection switch is opened or the hold in relay opens up for some reason.(like a bad relay getting hot).
Like I said this is from memory on this model from around 2012. So it may have changed.
Hope that helps.

This agrees with what was posted prior and tested earlier. I installed a light bulb on the hood and wired it to the ground and hold in circuit, and watched the light as it was dying. Never did the light ever flicker or go out as the engine died, and only went out when I turned the ignition off.

 

[Diggin It]

My only though there is that it's possible the voltage fluctuated )bad connection somewhere) enough to let the solenoid drop without you being able to see a difference in the lamp. A recording VOM might confirm or refute that.

I was going to suggest powering the solenoid separately about the time you mentioned it.

 

[Mike VS]

My only though there is that it's possible the voltage fluctuated )bad connection somewhere) enough to let the solenoid drop without you being able to see a difference in the lamp. A recording VOM might confirm or refute that.

I was going to suggest powering the solenoid separately about the time you mentioned it.

It sure can't hurt trying the separate power connection.

 

[ruffdog]

My only though there is that it's possible the voltage fluctuated )bad connection somewhere) enough to let the solenoid drop without you being able to see a difference in the lamp. A recording VOM might confirm or refute that.

I was going to suggest powering the solenoid separately about the time you mentioned it.

Yeah, that is what I was wondering too. If a bad relay would interrupt the hold circuit just for a moment, a person may not notice the test bulb flickering but the solenoid now shut the fuel off.

 

[Mike VS]

Yeah, that is what I was wondering too. If a bad relay would interrupt the hold circuit just for a moment, a person may not notice the test bulb flickering but the solenoid now shut the fuel off.

I think we are starting to narrow this down. A bad relay would definitely be realistic if it only had to flicker for a stall. How do I find out if and where there is a relay controlling the solenoid?

 

[Diggin It]

It might not be a relay. It might be a bad connection in a harness. I think you said something about looking at the connector surfaces, but we've seen threads where those checked good, but a wire inside the connector crimp was bad. Or inside the wire insulation itself. Have you closely inspected the wire harness for nicks, chafes or rodent chews?

The time thing still fries my cookies though.

 

[Mike VS]

It might not be a relay. It might be a bad connection in a harness. I think you said something about looking at the connector surfaces, but we've seen threads where those checked good, but a wire inside the connector crimp was bad. Or inside the wire insulation itself. Have you closely inspected the wire harness for nicks, chafes or rodent chews?

The time thing still fries my cookies though.

Ok, the connector for the solenoid (half of it) is new and the other half was clean as a whistle but there has to be several other connections further down the line. Love to know if there is a relay though, maybe I'll go out there and look around at it.
And the timing thing kind of makes sense too... Like a thermister heating up and losing connection momentarily.

 

[Diggin It]

You know, I hate to say it .... but ......

I haven't seen a schematic, but I saw the theory of operation on one of the first few pages. That referenced key switch rotation to activate the pull and hold circuits. We've seen more than one thread here in recent months where a bad contact inside the key switch did things no one would have expected.


Try the separate power bit direct from battery to the Hold circuit first ... before you do anything else like pulling the solenoid. Let us know how that checks out.

 

[Myz28u]

I’m not certain but the relays may be in the circuit board under the dash. It’s been a minute since I’ve had to work on one of these. If it’s on the board they may or may not be replaceable. May have to get the whole board. If it not in the board then the relays should still be under the dash area.
I remember the gas version has a circuit board with a time delay module for shutting off the fuel in the efi but I can’t say for certain in the diesel version if it’s integrated.

 

[Myz28u]

If I remember correctly the black side panel comes off where the hood and dash meet. It thinks it back in there. Hope that helps.