To find it with certainty, you should:
1. Consult your owner's manual: This is the best resource. The manual will show a diagram of your specific vehicle's fuel system, including the filter location.
2. Use a repair manual: A Haynes or Chilton repair manual for your specific year and engine will have detailed diagrams and instructions.
3. Search online for a diagram: Search using terms like "1997 Ford E-250 [engine type] fuel filter location diagram." Replacing the fuel filter is a common task, so many diagrams are available online. Make sure the diagram matches your engine type (e.g., 4.2L V6, 4.6L V8, 5.4L V8, 7.5L V8).
4. Look carefully along the frame rails: Start near the fuel tank and follow the fuel lines. The filter will likely be in a relatively accessible spot, often with a clip or strap securing it.
Warning: Working with fuel lines and fuel is dangerous. Be very careful, and if you are uncomfortable doing this yourself, take it to a mechanic. Fuel is flammable and potentially explosive.