Oops, the Cummins Won't Shut Off!

We all dread the moment when the diesel won't start.  Recently John Dann, Cielito #51, had the opposite experience; he turned his ignition switch off and his Cummins just kept purring.

The Lucas CAV's fuel shutoff solenoid

Interestingly, John reports there are no problems starting or shutting down the engine when it's cold.  Only if the engine is allowed to warm up does the problem occur.  So, what could cause this?  A logical explanation is that heat is causing the Lucas CAV injector pump's fuel cutoff solenoid to stick open.  The solenoid is critical to the engine's operation and so it's worth knowing something about it.  

The Lucas CAV's fuel shutoff solenoid clicks when the 
ignition switch is turned on

The fuel cutoff solenoid is nothing but an electrically operated valve.  Supply it with 12V and the valve opens.  Take away the voltage and it closes.  Aboard our tugs 12V is applied to the solenoid whenever the ignition switch is turned on.  Likewise, turn the ignition switch off and the solenoid closes.  A closed solenoid will stop the engine dead.  This is exactly what happened on Nellie D. #63 while cruising the ICW just north of Ft. Pierce, FL.  One moment the engine was running, the next it wasn't.  The single wire that supplies 12V to the fuel cutoff solenoid had vibrated off.  The result from the wire coming off is is akin to turning the ignition switch off: dead silence! 

The manual shutoff is the smaller lever on top, to the left
of  the larger throttle lever is

So, how do you shut down a Cummins when the ignition switch doesn't work?  It's simple.  Rotate the Lucas CAV's manual shutdown lever.  It's the small, spring loaded lever located on top of the fuel injector pump and just forward of the throttle lever.   

(All Diagrams are from the Cummins B Series Service Manual)