The Powerstroke diesel was a new engine for a new millennium, so little like diesels of 50 years past that it might have been from another planet. The Powerstroke 7.3-liter was beloved in its time not just because it was powerful and sophisticated, but because it was one of the great beasts of the new diesel era.
Among the many innovations introduced to consumers on the Powerstroke were revolutionary, hydraulically actuated electronic unit injectors -- or HEUIs, for short. HEUI injectors used high-pressure oil to shove fuel into the engine's combustion chambers, which did a lot of things. First, it allowed a computer to precisely control injection timing; second, it eliminated the need for the incredibly powerful and complex mechanical injection pumps that diesels had used for a century before.
Prior to 1999, the Powerstroke used a mechanical, engine-driven "lift pump" that sucked fuel from the tank and sent it to the HEUI injectors. Afterward, Powerstroke trucks used electric fuel pumps. You can find the pump relay in a fuse panel box under the hood. Look on the passenger-side fender well, and you'll see two boxes; in the box nearest the outside of the truck, the fuel pump relay is the one closest to the outside edge. It's a standard Ford relay, part number F57B-14B192-AA, available from any auto parts store.
If you're losing power to the fuel pump and find the relay working, check out the fuel pump's inertial cutoff switch behind the passenger-side kick panel. This switch cuts power to the pump after a collision. If the switch has been tripped, you must reset it; if it's failed, you must replace it.
