I hope you meant 4.0 inline 6 instead of a Ford 4.0 V-6
Any ways the crank sensor is a common problem. It is located on the drivers side at the top of the bell housing to the tranny. The other end is right behind the valve cover on the passenger side where it goes into the wiring harness. I have seen where the wires rub and cause them to quit working. I would check that. Worth a try I suppose.