Aloha Capt Rich,
I don't know a thing about the 140-143 volt problem except I had it happen at about 160 volts on a big Honda generator
once and it turned out to be the regulator
and needed to be replaced.
There are so many reasons for your 5KW to shut down. It could be anything from a short in the wiring
to your solenoid actuated fuel
switch, an air leak in your fuel pickup line. I would suspect if you are not getting the preheat to work there might be some faulty wiring
issues. When you try to start it does the lever arm on the fuel injection pump for the fuel shut off go to the open position?
I guess those would be a couple of places to start but always go for the simplest first, like clean fuel, filters and necessary voltage to your start system. Diesels of all makes need to have a pretty hefty spin in order to start.