Onan diesel gen problem

So we bought a new to us 2004 Holiday Rambler Endeavor. It has a 7500 Onan with 570 hrs. Picked it up yesterday. Gen started right up and ran perfectly. That was at 4PM. It ran non stop without problem till about 5AM. It just died, cranked on it 7-8 times. It would just spit and sputter, then started right up. Ran non stop till about noon today..Died, same thing spit sputter try to crank then fired up and ran for 15-20 mins died again, same thing, run for a few mins then die.. Finale started back up and ran no problems for 3 more hours. Pulled in the driveway..died..spit sputter..start back up. When you are trying to start it, it acts like its not getting fuel, lost prime or something. Any ideas??