have you done the filters lately,recommend ford filter on this,remove it,drain it and have a look for water in fuel or worse filings from the pump,have you had a code reader on it for a look at faults stored,did have one of these doing exactly the same thing at start of year,ended up getting an ignition switch and hasn`t looked back since but it is very difficult to say and would be guessing if this was what was wrong but would start with the fuel filter and take it from there,also check the fuel pipes for chaffing/rubbing in engine compartment,good luck
wickham
September 2010