Elusive Ignition Problem !

Hi guys. I'm new to this site so I hope I don't break any forum 'taboos' !

I have a problem with my 2004 Focus 1.8 petrol. 

My car suddenly started to lose power and when I stopped , it ran really 'lumpy'

The breakdown guy towed me home and then performed a diagnostic test which gave the error code P0351 and said it indicated a faulty coil. 

It turns out that I have no spark on cylinder number one so I checked the resistances in the coil and the HT leads which all seemed to be satisfactory (according to my Haynes manual) leading me to suspect a faulty plug. 

When I removed the plugs , number one had an excessively large gap so I thought I'd found the problem but the problem was still there ! 

 Still being reluctant to blame the coil , I did some online research and discovered that the coil in my wife's 2004 Fiesta  shared the same specifications as the coil in my Focus , so I temporarily swapped them over together with the HT leads.

This made no difference at all ! My wife's Fiesta ran perfectly well with my coil and HT leads and my car still failed to run properly using  her Fiesta's components so I'm now assuming that if my coil and HT leads work perfectly well in my wife's car , they must be perfectly good !

I understand that these coils work on the 'wasted spark' principle and that one coil operates plugs 1 and 4 and the other coil operates plugs 2 and 4. Surely this means that if plug 4 is firing , then the fault can't possibly be the coil , the wiring between the coil and ECU , or the coil 'switching' mechanism in the ECU itself (coil drivers) , otherwise NO plugs would fire OR only 2 and 3 would fire !

I'm totally baffled by this !

Any advice would be so very gratefully appreciated !

   Many thanks ! 🙂