My FTO GPX recently hit the 100,000 km mark and I thought I'd get the spark plugs changed and I also decided to get the leads changed. Ever since changing the spark plugs and leads, one of the spark plugs isn't firing up and hence when you drive, the car is loosing power and therefore its undrivable.

We tested the cylinder compression, tried putting the old plugs and leads on and still the same issue. I'm not sure what is happening there. Anyone have any ideas or experienced the same thing before?

Any help would be appreciated.