Shutting Down M817 Question

[817hunter]

I have a 1972 M817 which apparently shuts down by way of a dash-mounted handle/cable that shuts the fuel off. I previously had a 1978 M817 which did not have this feature, and I shut it down by turning both the Battery and Run switches to the off position. On the 1972, even if I turn off both switches the rig still runs without a hiccup, until engaging the fuel shutoff. Does anyone know which method is better, or why the 1972 would still run with both switches turned off?

 

[M35A2-AZ]

Sounds like the fuel shutoff solenoid on top of the IP pump is not working.

 

[Ajax MD]

Correct, the solenoid isn't working. The normal shutdown method is to turn off the "Run" switch first, then the "Battery" switch.

 

[817hunter]

Correct, the solenoid isn't working. The normal shutdown method is to turn off the "Run" switch first, then the "Battery" switch.

Thanks to both of you for the direction to go in!

 

[CGarbee]

As the above responses have stated, fuel is bypassing the cutoff solenoid.
Most likely because someone has screwed in/out (I never can remember the direction) the knob that bypasses the cutoff solenoid...
Often done when someone is having electrical issues (weak batteries/weak charging/too much load for the output of the alternator (my issue when towing stuff with the M816 with all the lights including the tow lights on...).

Try turning the knob so that it is using the solenoid instead of the bypass to see if it works, it should be pretty obvious after that how to proceed in diagnosing the issue and deciding upon a resolution...

 

[MyothersanM1]

This screw...

 

[Ajax MD]

This screw...
View attachment 856490

This is one of those things that has been covered in the forums that I really need to scribble down in a small notebook and keep in the map box in the cab. I'll be sitting on the roadside one day thinking "I know I read about this but I can't quite remember what to do..."

 

[fasttruck]

You turn the screw clockwise to bypass the fuel solenoid and counterclockwise for normal electrical operation. It doesn't turn too many revolutions from one extreme to the other. With a stick shift truck like a M 817 you can put it in high gear and stall the engine to stop it if you don't want to go under the hood and reset the fuel shut off valve. You have to wonder what was going on to have someone put the fuel solenoid in bypass. All 809 series trucks were born with the hand operated emergency shut off. If you had one without probably the previous owner removed it to prevent unqualified drivers from accidentally using it. When the 809s came out in the early 70s the Army had a lot of trouble with drivers using the emergency shut off and not resetting it manually as the previous M39 series trucks had a cable operated shut off for their Mack or Continental engines where the fuel shut off was also cable operated but did not have to be reset on the engine.

 

[doghead]

If there was only a book with the basic operating instructions….

 

[817hunter]

As the above responses have stated, fuel is bypassing the cutoff solenoid.
Most likely because someone has screwed in/out (I never can remember the direction) the knob that bypasses the cutoff solenoid...
Often done when someone is having electrical issues (weak batteries/weak charging/too much load for the output of the alternator (my issue when towing stuff with the M816 with all the lights including the tow lights on...).

Try turning the knob so that it is using the solenoid instead of the bypass to see if it works, it should be pretty obvious after that how to proceed in diagnosing the issue and deciding upon a resolution...

CGarbee - thanks! Didn't know what the knurled knob on the solenoid was for, but will now start my look into things with that.