For you diesel guys. Cat D3, 1979. Brother was in the woods, was running fine, then began like it was running out of fuel or lost a cylinder like running on 3 instead of 4. Has fuel in it 60%. It quit running would restart run rough, shut down, and now just won't start. Your thoughts.

Start simple, can you hear fuel pump kick on, if so fuel to the filter, then fuel past the filter. If no to the above sounds like possible injection pump. If you've let the fuel sit in the tank for a while this newer fuel grows algae fairly quick.

I have about the same vintage D3. Running good and then wouldn't rev and would quit. Issue was plugged up fuel filters. Cleaned the fuel line and replaced both filters. No problems since.

Fuel issue. Injection pump? Crack the lines at the injectors and see if fuel is spitting out at each one.

I say change the filters. Make sure you got good fuel flow through the lines. If it completely starved, you might need to crack lines loose at injection nozzles about 2 turns, crank engine until you see bubble free fuel squirter up