The check ball on the 7.3L engine’s high-pressure oil pumps generally goes into the oil line fittings. It is a plastic check ball that’s held in its place by the “Serviceable Plug” situated underneath the HPOP. This is the original check ball that can be found in all 7.3 diesel HPOPs from 1994 to 2003. It may crack over time, resulting in a “No Start” problem. This ball can get damaged when changing the serviceable plug.