The injection pump rotor, or pump component that connects to the crankshaft in the distributor section, can seize or lock up due to lack of pump lubrication. This lubrication shortage often results from a clog in the pump. Under such circumstances, the pump and fuel filters should be checked for clogs and lubrication should be added.
The diesel lift pump contains a diaphragm which fills with oil. A ruptured diaphragm causes the pistons to vibrate and ultimately wear down. This results in fuel bypassing the injection pump altogether, causing low or nonexistent fuel pressure. Replacing the diaphragm and any worn pistons is necessary to restore proper injection pump function.
Air entering the fuel lines due to cracks, leaks or other entry points results in excess air being pumped by the injection pump. This leads to fuel pressure loss, which can cause an engine to stall or not start altogether.