D2 4U main engine wont start

Check to see if your governor control lever hasn't "over-centered" in the shutoff position. It's meant to be a shutoff detent, but can be mistaken for actual operation position because there is still a range of travel after the "over-center" point of resistance. Give the lever a good hard pull in each direction and you should feel what I'm talking about. If I remember correctly, when the lever is rotated clockwise as far as it will go (I'm talking about the small lever on side of the governor housing that the throttle linkage attaches to) it is at full throttle. Counter-clockwise rotation until it hits the "over-center" point of resistance is idle, and further counter-clockwise past the "over-center" is the detent shutoff position. The lever will still travel further counter-clockwise from this point, but the rack won't flow fuel at sufficient enough pressures or volume for injection when in this range.

So to make a long story short, before you try to crank the diesel engine again go and pull the throttle lever to what feels like full throttle, then grab the governor housing lever and see if it will "over-center" and rotate further. If it does, try to start the diesel on that side of the detent and see what happens. Just something simple to check before taking anything apart.

Take the side cover off the injection pump and check and see that you have rack movement with throttle movement. The rack has been known to stick and there is only spring coupling between the two.