went to look at a fiesta 1.4 16v today no spark on 3 so changed the coil pack for a new one ran fine for 2 mins then lost spark on cylinder 1 and 4 , so fitted the old one back on and the same no spark cylinder 3.
I'm guessing faulty coil pack?

 

Sounds like it, change the plugs too. If the electrode is damaged causing too much resistance through the plug, then it will burn out the coil pack in no time.