Help for a new m936 owner please...

[JRMMD]

Hello all.
I am a very new m936 owner (as in yesterday). Bought a 1984 wrecker and drove it about 80 miles before it decided to die on the road. A very expensive tow last night and it is at least at the farm where I can slowly investigate and become much more familiar with this newest toy.

I'm fairly well schooled with my automotive stuff, my tractor, and my backhoe. But clearly this beast is a different kind of animal.

I have a simple, newbie question that will really help with my initial troubleshooting...

Assuming full batteries and a broken neutral starter safety switch, if the battery switch is ON and I turn the ignition switch from OFF to RUN (but not to START), should the dash still get power (warning buzzer, parking brake light, etc)? I know the neutral start switch would prevent the ignition's START position from engaging the starter, but I have looked everywhere to see if a faulty neutral switch prevents the ignition switch from essentially "working" at all, or if it only affects the START position.

Likewise, I am trying to figure out if there are other safety switches to check that would explain why I have a full charge but get nothing from the ignition switch.
I know the switch itself could be shot but just trying to learn the basics.

For example, my tractor won't attempt to start if the PTO is engaged, the hydrostatic is in gear, or my fat butt isn't in the seat.

If anyone can help me out on this I would appreciate it.

I'm learning it as fast as I can and look forward to learning from this site.

Jim

 

[Mullaney]

Hello all.
I am a very new m936 owner (as in yesterday). Bought a 1984 wrecker and drove it about 80 miles before it decided to die on the road. A very expensive tow last night and it is at least at the farm where I can slowly investigate and become much more familiar with this newest toy.

I'm fairly well schooled with my automotive stuff, my tractor, and my backhoe. But clearly this beast is a different kind of animal.

I have a simple, newbie question that will really help with my initial troubleshooting...

Assuming full batteries and a broken neutral starter safety switch, if the battery switch is ON and I turn the ignition switch from OFF to RUN (but not to START), should the dash still get power (warning buzzer, parking brake light, etc)? I know the neutral start switch would prevent the ignition's START position from engaging the starter, but I have looked everywhere to see if a faulty neutral switch prevents the ignition switch from essentially "working" at all, or if it only affects the START position.

Likewise, I am trying to figure out if there are other safety switches to check that would explain why I have a full charge but get nothing from the ignition switch.
I know the switch itself could be shot but just trying to learn the basics.

For example, my tractor won't attempt to start if the PTO is engaged, the hydrostatic is in gear, or my fat butt isn't in the seat.

If anyone can help me out on this I would appreciate it.

I'm learning it as fast as I can and look forward to learning from this site.

Jim

.
There is a safety switch. Link below:

1986 M923 intermittent no-start condition

Looking for troubleshooting guidance and suggestions on resolving this intermittent no-start condition. The issue only started on July 3rd, when we were prepping the truck to participate in some Independence Day operations. The truck is a 1986 AM General M923 with the ABS system. It has the...

www.steelsoldiers.com

 

[doghead]

What happened when it quit?

 

[JRMMD]

Thank you for a quick reply. I searched the site before posting but didn’t see this.

 

[Mullaney]

Just because...

Welcome to the group! Hate to hear that you had trouble with your M936. Definitely isn't cheap if you can't move yourself toward home
Seems strange that everything was fine and it just "quit". There is a PCB box on the firewall that might have rolled over and died rather than
the neutral safety switch. That info is also in the thread I sent earlier.

The good part is that the guy who answered the questions in the thread is also in Tennessee (Memphis).
He has forgotten more than I will ever know - so don't hesitate to ask questions of him (simp5782)

Good luck on your quest!

Tim
.

 

[doghead]

Do you know that you must shut it off with the “ignition switch” before turning off the battery switch? If you mistakenly shut the battery switch off first, you can damage the protective control box.

 

[JRMMD]

What happened when it quit?

Ran fine on interstate. I exited and it died on the ramp. Tried to restart and it turned over fine but wouldn’t fire. Let it sit for a bit and tried to start but then it wouldn’t even power the dash or started (symptoms stated above). Let sit longer, it turned over and started. Drove another mile and it started losing power under a hill strain at about 30 mph. Petered out and died on side of road. Repeat essentially the same behavior as happened at the exit ramp and it started again. Drove half a mile and sputtered out again under a hill load. But then wouldn’t even try to turn over (no dash power, warning buzzers, nothing.
I hear the relay kick on under the dash when I turn on the battery switch and lights, etc still work (I know it’s low power drain). But the batteries read good voltage with manual meter.
Likely multiple issues. Full tank of gas on right which was the tank I was pulling from but I found that both right tank vent hoses were broke last night too.
So, I’m thinking both an electrical issue and probably poor fuel delivery.
I have a lot to investigate.

 

[simp5782]

Bad pcb. Smack it with a hammer if you need it to work.

Rebuild it afterwards.

It's the black box behind the washer bottle on the drivers side of the engine bay.

Pcbs go on the fritz during hot and cold snaps in weather generally

Fuel vents won't cause any issue like you had. Especially broken

Where in TN are you?

 

[JRMMD]

Bad pcb. Smack it with a hammer if you need it to work.

Rebuild it afterwards.

It's the black box behind the washer bottle on the drivers side of the engine bay.

Pcbs go on the fritz during hot and cold snaps in weather generally

Fuel vents won't cause any issue like you had. Especially broken

Where in TN are you?

 

[JRMMD]

I will happily go after it with a hammer.
Definitely anxious to learn more about the truck and put it to work.
I will definitely research the PCB and learn more about it. Thanks!
The truck/farm is in Lawrence County and I work out of Nashville - so basically up and down the central part of the state.

 

[JRMMD]

Do you know that you must shut it off with the “ignition switch” before turning off the battery switch? If you mistakenly shut the battery switch off first, you can damage the protective control box.

I can't deny I may have made this mistake.
For what it's worth, it died on the exit before I would have had the chance to do that - because they had it started when I got there to pick it up. But I certainly could have screwed it up thereafter. In desperation to get it started, I was probably careless.
It's things like that I worry about the most - messing up sequences/switches/etc that you guys otherwise know so well.

 

[simp5782]

Screw the combat knob in on the fuel solenoid on top of the injection pump. Then jump the starter with a screw driver and see if it runs. Or attempts to

Try chasing one issue at a time. This will eliminate it being an electric issue that caused the shut down

 

[fasttruck]

Pic of Cummins PT Fuel pump attached. Fuel solenoid which turns fuel on or off to start/shut engine off is on top of pump. Has knurled knob facing front of truck. Normal operation is turned out. For bypass operation as when there is no electricity to the solenoid available, turn knob in to hold fuel valve open. To shut engine down either: 1) turn screw out, 2) use emergency fuel shut off on dash. This will require you to go under hood and reset the valve by hand, or with a M809 series truck, put it in high gear and stall the engine. If you can get the engine started it will run in bypass until you shut it off or it runs out of fuel.

 

[JRMMD]

Really appreciate the initial help on the PCB!
I smacked the snot out of it and it, in fact, restored power to the ignition switch. So, at a minimum, the engine is trying to turn over again.

I didn't see the post about the fuel bypass screw until after I was no longer at the truck. So, I will try that out next time to see if it starts.
I did try cranking it a bit but it wouldn't start. It just turned over.
I assume a bad PCB could not only cause the truck to not turn over, it could also affect fuel delivery even if the truck does turn over...?
If that is true, and the truck starts with the screw adjustment, would all of these issues point to the PCB?

I fell like it's probably worth replacing the fuel filter. Even if that isn't the issue, I suspect my current one is old.

Thanks again, guys!

 

[WildernessJeep]

Really appreciate the initial help on the PCB!
I smacked the snot out of it and it, in fact, restored power to the ignition switch. So, at a minimum, the engine is trying to turn over again.

I didn't see the post about the fuel bypass screw until after I was no longer at the truck. So, I will try that out next time to see if it starts.
I did try cranking it a bit but it wouldn't start. It just turned over.
I assume a bad PCB could not only cause the truck to not turn over, it could also affect fuel delivery even if the truck does turn over...?
If that is true, and the truck starts with the screw adjustment, would all of these issues point to the PCB?

I fell like it's probably worth replacing the fuel filter. Even if that isn't the issue, I suspect my current one is old.

Thanks again, guys!

You can rebuild the PCB yourself. Mine was bad when I got it, as well. You just need to order two of these and get a screwdriver:

https://www.amazon.com/dp/B001FQMZO2/ref=cm_sw_em_r_mt_dp_VZNRDF8P2G4TY701S942?_encoding=UTF8&psc=1

 

[Goliath P. Jones]

How

You can rebuild the PCB yourself. Mine was bad when I got it, as well. You just need to order two of these and get a screwdriver:

https://www.amazon.com/dp/B001FQMZO2/ref=cm_sw_em_r_mt_dp_VZNRDF8P2G4TY701S942?_encoding=UTF8&psc=1

How does one go about rebuilding the pcb box? I can't believe that I accidentally screwed up and shut down the battery switch first. Now the truck is struggling to start, and not turning over strong. Dragging to start. I was driving it to get several yards of soil, shut it down incorrectly, caught myself as it was happening and tried to turn the switch back on. Immediately following it was struggling to start.

 

[simp5782]

How

How does one go about rebuilding the pcb box? I can't believe that I accidentally screwed up and shut down the battery switch first. Now the truck is struggling to start, and not turning over strong. Dragging to start. I was driving it to get several yards of soil, shut it down incorrectly, caught myself as it was happening and tried to turn the switch back on. Immediately following it was struggling to start.

 

[Goliath P. Jones]

Thank you very much simp5782, that's exactly what I was needing. Looks like I will be ordering the parts and rebuilding the pcb unit. Now I just need to find a second unit to rebuild it for a spare.

 

[WildernessJeep]

How

How does one go about rebuilding the pcb box? I can't believe that I accidentally screwed up and shut down the battery switch first. Now the truck is struggling to start, and not turning over strong. Dragging to start. I was driving it to get several yards of soil, shut it down incorrectly, caught myself as it was happening and tried to turn the switch back on. Immediately following it was struggling to start.

It's really pretty simple. Pull the old box down with a couple of half inch socket wrenches. Unplug it from the truck. Pry the box lid off with a flat tip screwdriver. Replace the two starter solenoids Inside the box wire for wire. Very simple process, should take a couple of hours at most.

 

[Goliath P. Jones]

It's really pretty simple. Pull the old box down with a couple of half inch socket wrenches. Unplug it from the truck. Pry the box lid off with a flat tip screwdriver. Replace the two starter solenoids Inside the box wire for wire. Very simple process, should take a couple of hours at most.

I ordered the solenoids from Amazon prime, the parts are on their way and are supposed to be here tomorrow.