No power from cylinder 5?

I have a 1993 XJ6 which was purring till yesterday, the engine had developed a slight lumpy wobble and a a bit more of a popping coming out of the exhaust, I thought this was just a spark plug gone on that cylinder as there was no difference in engine wobble or power when I removed the lead from the plug
I replaced the plug today and there is still no difference I tested the leads to and there all fine, I had been removing a car phone kit previously which required the fascia from the centre console to be removed, I know this not may seem relative but I do know how complex the electrics on jags are and wondering if there are any engine management looms passing through there, just in case I damaged or pulled something out.
Or is it more likely something under the bonnet