Where is cylinder number four located on a 1998 5.4 ford expedition?

On a 1998 Ford Expedition 5.4L engine (Triton), cylinder #4 is located on the passenger side, towards the rear of the engine. It's not the furthest back cylinder on that side, but it's relatively close to the back.

To be absolutely sure, you should consult a repair manual specific to your vehicle's year and engine. The firing order can sometimes affect how cylinder numbering is spatially arranged. A diagram in the manual will clearly show the location.