HI, not sure if still needed for this post, but I DID experience a mysterious misfire on 2 cylinders on my 1.8 zetec Focus. The problem was flash-over, on TWO of the plugs. These were all new plugs, and the problem was introduced (self inflicted if you like!) after using a cheap tool to replace them. I did not know that the plug-spanner had nasty rubber internal grip - for gripping the top of the plug - and it had a high metallic content, leaving black lines on the porcelain. This changed to a hard track line, once a few misfires occurred. Tick-over was OK, pull-away was awful. I fixed it by removing and cleaning all plugs (with a better plug spanner), and putting MAPLIN SILICONE GREASE on the porcelain parts, and any area in the plug dwell likley to hold moisture (Clean and blow clear with an air-line first). This stuff is used in HIGH VOLTAGE/EHT systems like CRT tube areas that have 20 to 30KV present, so is ideal on car ignition flash-over issues. Mine has been fine since I did this 18 months ago. TD.
