I don't have a MEP-006a, but do have a commercial Onan powered by a close relative of the same Allis Chalmers engine. Have you bled the diesel injectors to confirm you don't have air in the lines, and have you checked that you are getting return fuel from the return port on the top of the injection pump (it has a glass bead one way valve inside that can get gummed up) Mine uses a Roosa Master / Stanadyne DB or DC series injection pump (DCGFC-631 in the case of mine), these injection pumps have an internal kill solenoid which is powered by the 2 wires on the top of the pump, they also have 2 levers on the sides of the pump, one is governor speed setting for the internal mechanical governor (throttle cable would be connected here) and the other is an external kill switch. I am not sure is yours uses the internal solenoid or the external kill lever for shut down. I would suggest after careful surface cleaning to remove the side inspection window on the pump and check for "coffee grounds" which is sign guts are coming apart in the pump and it needs to be rebuilt, you may also want to remove the top cover on the pump as the kill lever sometimes sticks on these when stored and does not return to the run position if your not getting fuel past the injection point.
Ike
ps if you have to get the injection pump rebuilt be aware that parts for the DCGFC pumps are a bit more expensive and getting harder to find than the more common members of the DB family of injection pumps, when I had mine rebuilt 3-4 years ago I had to call several Diesel injection shops before I found one that would work on it, and they quoted me an extra $300 above their regular price for a DB series pump, ended up at almost $900 for the rebuild after adding unexpected parts that needed changing, this was on a running, but smoking low hour engine.
