Again, probably crud/rust in the shut off cavity in the injection pump. ' Usually ', injection pumps have a small screen right where the fuel line hooks up to the pump. This is to make a final effort to stop anything bad from getting into the pump, but won't stop moisture. Water can accumulate in the shut off valve area and cause rust/scale to build up. You may be able to clean out the shut off valve area inside the pump. You could also install some type of valve in the fuel line going to the pump which would shut the thing off. Most diesels had mechanical shut offs in the past, the electrics are something new. You need to address your water problem someday, too. Water in your tractors fuel system is like an STD, if you are doing your job you should never find it there.