I would say if you haven't done so already, check to see if there is spark coming from the plug wires. If you don't know how to do this, find someone who does. *DISCLAIMER: I am not responsible for any damage or otherwise harmful effects (example: death) as a direct result from you/anyone else attempting this maneuver!*
Have engine off. Disconnect one plug wire, preferably the first in firing sequence. Take a screwdriver, preferably a long philips (6-8"), and insert point end of screwdriver into the plug wire, assuring contact of screwdriver with the plug seat. Have a buddy or trusted individual crank the engine as you ground out the screwdriver (while it is still up in the plug wire) on something like the engine block or frame (if it is long enough). As SOON as you see/feel a spark, CEASE IGNITION START!!! Repeat step for each plug wire (only three more!!) and the one that doesn't spark or has a weak spark is your culprit. Or, if you'd like, take it into an Authorized Ford/Lincoln/Mercury service center (f*** a mechanic) and let them test your plug wires.
It may also be your plug gap. Check the owner's manual for the proper gap on your spark plug and adjust accordingly. Also, check if it is burning rich or hot, as this is also a cause for hesitation on start-up.take-off.