MCI 7 Safety shut off

[davejean]

I just tried starting my 1970 MCI 7 after being stored this winter.  It starts fine, but once the air pressure gets up a little the solenoid / air valve shuts off the engine.   Can anyone please tell me all the systems that would communicate to the solinoid/airvalve telling it to shut off the engine for whatever reason?
Thanks much

[bevans6]

The no-fuel lever on top of the governor is the engine shut-off lever with an air cylinder that presses on it.  It's controlled by a Skinner valve mounted on the upper left hand wall of the engine bay, through the rear doors.  The skinner valve is controlled by the two engine run/stop  switches, one on the dash that is called the master switch, and one on the rear control box.  The Skinner valve controls air flow to the engine stop air cylinder that pushes on the no-fuel lever.  The Skinner valves source of air in the auxiliary air system which is separated from the brake part of the air system by a pressure protection valve which only allows air to pass into the auxiliary system after the brake portion has reached around 65 psi of pressure.  What is happening is that the Skinner valve is either being told to shut the engine off by a switch in a wrong position, probably the rear switch, or a switch or electrical connection failure, or the Skinner valve is stuck in the open position.  After the engine starts and pressure starts to build it runs until air starts to move into the auxiliary air system.  As soon as the air pressure gets high enough the shut down cylinder moves over and presses on the no-fuel lever and turns off the engine.  The electrical setup for that Skinner valve is such that it must be told to close by a positive 24 volt signal on its terminal and that closes off airflow to the air cylinder that it controls.  Absent the positive 24 volt signal it will be open as a failsafe to keep the engine from running.  First thing to do is to set the master dash switch to on, set the rear switch to run, and check for positive voltage at the Skinner valve.  Depending on your engine controls and how stock or modified they are a number of automatic engine shut-down features could also tell the Skinner valve to shut down the engine.  Things like low coolant, high temperature, low oil pressure sensors, etc.

Brian

[luvrbus]

If you starting it from the rear the front switch needs to be in on

[Seangie]

Dave -  I had the same issue on my bus and it was caused by a faulty system shutdown device (Cadillac Controller)  It was wired in after the engine had been rebuilt right above the turbo (on the controller itself it said keep away from hot locations)

I pulled out the cadillac auto shutdown and never had a problem since.  Just gotta be smart when driving it and watch the temps on a long climb on a hot day.

If you search my previous posts youll see some info on it.

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org