sable starting problem

97 Sable 3.0 D.O.H.C has problems starting every so often, car just cranks and cranks, replace crankshaft position sensor and it fires right up. this car has had 3 sensors ( all Ford) in the last 2 years with the last one being just 2 months ago. On sunday it wouldnt start but a shot of quick start and it fired right up. Any thought to this problem? Lots of fuel preasure at test valve on fuel rail.

Thanks, Dave