Once you know the engine, you can then consult a repair manual specific to that engine and year of vehicle for the precise location. These manuals usually have diagrams showing the filter's location. You can find these manuals online or at auto parts stores.
Generally, however, the fuel filter on these older Ford diesels is often found somewhere along the frame rail, near the fuel tank, and easily accessible. But again, knowing the exact engine is critical for accurate location.
