Problems with M923 shut off solenoid

[Navy dude]

I bought a new solenoid to replace one that was inop. It is the solenoid that allows the engine to start (I took it off and have been overriding it with the emergency shutoff handle in the cab). I threw the new one on (Chinese part) and it worked a few minutes until it went up in heat and smoke! Question is.... Do you think it was a bad part, or is it possible I reversed the polarity at the connection? Otherwise maybe an electrical problem elsewhere? When I connected it I really couldnt tell if it was seated properly, but I connected it the way it most easily slid together. It was the 24V solenoid (at least it was marked 24V, from China, who knows?!). I am sorry if I don't know the exact name of the solenoid (Fuel Shutoff, starter shutoff, etc...) but it is the one that energizes to a compressed position, and spring loads a pin out to shut off motor when deenergized.

It initially worked great as I energized the Starter switch on and off, but then a massive short that fried the solenoid after idling for about 3 minutes! Everything seems ok otherwise still, I was afraid I might have caused electrical damage elsewhere.

Any help GREATLY appreciated before I buy another one. The truck is a BMY turbo...

 

[TruckGuy]

Check and see what voltage you get at the connector.

 

[74M35A2]

This one may be easy. The fuel cut solenoid has 2 coils and a ground. One coil is low resistance and powerful, heats fast and is for momentary uses as the "pull" coil. The other coil is the "hold" coil, and is higher resistance and made for continuous use powered by the ignition circuit.

I have not looked, you probably nuked the pull coil by having continuous current on it is the connector not being correct. Power for the pull coil comes from the motor side of the starter, so it should only be engaged during cranking.

The emergency stop cables pulls the same cam lever on the injection pump. Several people abandon the solenoid and use this only, and it works for them.

 

[Navy dude]

This one may be easy. The fuel cut solenoid has 2 coils and a ground. One coil is low resistance and powerful, heats fast and is for momentary uses as the "pull" coil. The other coil is the "hold" coil, and is higher resistance and made for continuous use powered by the ignition circuit.

I have not looked, you probably nuked the pull coil by having continuous current on it is the connector not being correct. Power for the pull coil comes from the motor side of the starter, so it should only be engaged during cranking.

The emergency stop cables pulls the same cam lever on the injection pump. Several people abandon the solenoid and use this only, and it works for them.

Thank you! Even I can understand this explanation. If I get another part, any clue as to how I can determine which side is which? There doesn't seem to be any obvious connections that match up on the harness. I noticed that when I had installed the solenoid, it energized when I turned the start switch one position short of cranking the engine (when you get the click click click before cranking) From your explanation, the solenoid should only energize when the engine is actually cranking? Any further clue as to the correct polarity much appreciated.... Excellent info, thank you very much brother!

 

[74M35A2]

If your vehicle side harness wires are labeled, it should be gravy. See attached. Wire #54 is +24v fed from ignition switch to the run or hold solenoid, wire #82 is fed from the starter motor solenoid to the pull solenoid, and wire #94 is ground for both. If not labeled, use a volt meter to sniff for 24v with the ignition switched on, and the other should show 24v during actual cranking. Third wire is ground.

If you use an ohm meter on your next solenoid connector, the lower resistance coil will be the pull coil (connect to #82), and the higher resistance coil will be the hold coil (connect to #54).

If your solenoid pulled back as soon as you flipped the ignition switch on, you melted the pull coil as expected from improper connection. The solenoid should only retract during actual engine cranking, and then stay retracted once released to the run position (hold coil active).

Pic attached, click to enlarge and clarify:

 

[Navy dude]

If your vehicle side harness wires are labeled, it should be gravy. See attached. Wire #54 is +24v fed from ignition switch to the run or hold solenoid, wire #82 is fed from the starter motor solenoid to the pull solenoid, and wire #94 is ground for both. If not labeled, use a volt meter to sniff for 24v with the ignition switched on, and the other should show 24v during actual cranking. Third wire is ground.

If you use an ohm meter on your next solenoid connector, the lower resistance coil will be the pull coil (connect to #82), and the higher resistance coil will be the hold coil (connect to #54).

If your solenoid pulled back as soon as you flipped the ignition switch on, you melted the pull coil as expected from improper connection. The solenoid should only retract during actual engine cranking, and then stay retracted once released to the run position (hold coil active).

Pic attached, click to enlarge and clarify:

View attachment 648690

Perfect. Got it, very much appreciated.....

 

[WillWagner]

I posted all the diagrams in another post, let me see if I can find them.....

 

[WillWagner]

Here is one with the spec for pull in length of the plunger,

http://www.steelsoldiers.com/showthread.php?159105-M939-Does-not-Idle

 

[Navy dude]

Here is one with the spec for pull in length of the plunger,

http://www.steelsoldiers.com/showthread.php?159105-M939-Does-not-Idle

Excellent, thanks so much!

 

[WillWagner]

Sorry it took a bit, but here are the resistance specs and what wire is what chart....

 

[74M35A2]

Nice grab. That will be usedul going forward.