M939A2 5 Ton No Start / No run

[pumpkin]

No Start /No run , Ignition switch checks good , it takes twenty or more tries with the ignition switch before it will crank/run? M939 A2 1991 BMY 8.3 Cummins

 

[98G]

Beat on the PCB....

 

[swbradley1]

It might not be getting a good ground on the PCB. Mine was flaking out until I pulled the cover (mine isn't full of epoxy) and I just put the cover back on and put wire ties on it to hold it down better.

Or buy a good takeout from the want ads.

 

[74M35A2]

Yep to both. You can rebuild yours with 2 new 24v solenoids as another option.

 

[fuzzytoaster]

I've got tested used PCBs in the classifieds as well. Plenty of options out there to tackle this common problem.

 

[infidel got me]

Got a spare on my work bench (thanks F.T.) That box can go out on you at any time.

 

[74M35A2]

It can. I took an old PCB, removed the bottom connector, and jumpered the power solenoid wire on it. If mine ever goes to lunch unexpectedly, I can simply unplug my PCB and plug this jumpered connector in and everything will work. My gear reduction starter has a relay on it so it only needs to be fed low current from the dash switch to activate. Can stop the engine with the emergency cable, and just need to unplug this mate to depower the dash. I would recommend this to anybody who is going to ditch their "bad" PCB. Cut the connector out, send it to me, or the entire PCB, and I'll make you the same for free and send it back to you, or tell you how to do it. Good piece of mind to have onboard.

 

[Scar59]

It can. I took an old PCB, removed the bottom connector, and jumpered the power solenoid wire on it. If mine ever goes to lunch unexpectedly, I can simply unplug my PCB and plug this jumpered connector in and everything will work. My gear reduction starter has a relay on it so it only needs to be fed low current from the dash switch to activate. Can stop the engine with the emergency cable, and just need to unplug this mate to depower the dash. I would recommend this to anybody who is going to ditch their "bad" PCB. Cut the connector out, send it to me, or the entire PCB, and I'll make you the same for free and send it back to you, or tell you how to do it. Good piece of mind to have onboard.

Neat Idea, will this "jumper" connector work on both M939 and M809 trucks? It would be handy to keep in the travel tool bag.

 

[74M35A2]

I am not an 800 expert, but it should if it work the same. On an M939, the PCB ha 2 solenoids in it. One is for dash power, and the other is for starter engagement power feed (so dash switch is low current). For the dash battery power solenoid in the PCB, you simply connect a large wire between what would be both large terminals of that solenoid, but you jut do it on the box ide of the connector, and throw everything else away. For the starter one, connect the smaller PCB starter solenoid trigger wire directly to the larger PCB starter solenoid output wire going to the starter, but don't hold the dash crank switch down long or it could get warm and fail. Or, you could jut leave a loose end going to the starter that you touch it' end to the dah power jumper, and this would crank the engine from underhood. Remember, this is for emergency use only, and your dash power will stay on as long as it is connected, or until the batteries die. I should probably just draw it out instead.

s button does not work on my computer !!! Using copy-paste so font gets trashed.

 

[73m819]

I am not an 800 expert, but it should if it work the same. On an M939, the PCB ha 2 solenoids in it. One is for dash power, and the other is for starter engagement power feed (so dash switch is low current). For the dash battery power solenoid in the PCB, you simply connect a large wire between what would be both large terminals of that solenoid, but you jut do it on the box ide of the connector, and throw everything else away. For the starter one, connect the smaller PCB starter solenoid trigger wire directly to the larger PCB starter solenoid output wire going to the starter, but don't hold the dash crank switch down long or it could get warm and fail. Or, you could jut leave a loose end going to the starter that you touch it' end to the dah power jumper, and this would crank the engine from underhood. Remember, this is for emergency use only, and your dash power will stay on as long as it is connected, or until the batteries die. I should probably just draw it out instead.

s button does not work on my computer !!! Using copy-paste so font gets trashed.

One solenoid IS the master switch, it powers EVERYTHING, not just the dash, the other solenoid is the start solenoid, on the 809 series there is 1 safety switch ( engine run oil pressure switch, that needs to be closed (no oil pressure) to allow the solenoid to engage so the starter can be used, on the 939 series, there are two safety no run switches that have to be closed for the solenoid to engage, one is the engine run switch and the other is the neutral safety switch.

You CAN use a 939 PCB on a 809 series truck BUT you CANNOT use a 809 series PCB on a 939 series truck.

 

[wreckerman893]

Are you sure the fuel shutoff solenoid is allowing the fuel to flow? These trucks are notorious for the solenoid to de-energize and not start. Usually resulting in the operator draining the batteries. Sometimes extended cranking will eventually get the solenoid to energize but it is hard on the batteries. If you are alone up can zip tie it open and the truck will crank. Remember to cut the zip tie or it will not shut off.

 

[Tornadogt]

yes the "jumpers" do work on M809series trucks also...
This thread is great info on the Boxes and emergency jumpers Specifically post #26 for the jumpers
http://www.steelsoldiers.com/showthread.php?113634-Ever-see-inside-the-Protective-Control-Box

 

[pumpkin]

Thanks for the help guys , I spent all day with the M939 A2 removed control box and opened it up two solenoids and a printed circuit board , tested solenoids with jumper cables ,put it back on the truck and every thing works as designed , I blame it on a bad ground on or near the control box ,Thanks again for pointing me in the right direction .

 

[pumpkin]

Thanks Guys I worked on m939 A2 all day removed the control box and opened it up two solenoids and a printed circuit board tested solenoids with jumper cables - ok - reinstalled control box and the truck started and run as designed I blame it on a bad ground on the wires that bolt on the control box . I also installed a 24 volt battery tender so the batteries will stay charged . Thanks guys for pointing me in the right direction !

 

[datadawg]

Beat on the PCB....

If my 932a2 is cranking but not starting, should I try that or is "beating on the pcb" only for no crank condition?
Where on the pcb would I hit and how hard? Repeatedly or just once and retry starting??

 

[Tornadogt]

If my 932a2 is cranking but not starting, should I try that or is "beating on the pcb" only for no crank condition?
Where on the pcb would I hit and how hard? Repeatedly or just once and retry starting??

If it cranks and doesn't start it is a fuel issue, (not PCB related). Check the fuel shutoff solenoid, make sure it is opening/add fuel/ bleed fuel system. (on a A0-A1 250 Cummins also check that the emergency fuel shut off was not used, if it was, you have to manually rest it under the hood)