I just rebuilt an 05 cummins due to a dropped valve seat. I replaced all the piston rings, one piston, new head, all new bearings on everything by the customers orders. I got everything back together and started it. It showed oil pressure on the gauge but then dropped to zero. So i hooked a mechanical guage up and still had no pressure. So i thought maybe the mechanical is bad....i took the line off the housing and started it....NOTHING came out.. I then replaced the oil filter thinking it was a bad oil filter even though it was brand new...still didnt cure the problem... Does anyone have any ideas??? I need to have the truck done as soon as possible as college ended last week and im still working on it at the college. Thanks guys!