Coilpacks are very prone to giving up, around £35 new from ford, have a look at the plugs also, in case they are bosch, if so bin them and use fords own, also have a look at the porcelain part of the plug to see if it has streak marks like jagged lightening going from the main metal body to the top, a orangey ring is normal if present but no streaking this indicates it is leaking(electrically) another common zetec problem, cured by using silicone brease on the inside of the plug boot where it goes over the plug.
Other things to look at include fuel filter if old, is the MAF dirty, clean with carb cleaner if it is, don't under any circumstances poke it with anything, this will break it.
tabetha