Easy, but you need a plug spanner (preferably magnetic) which has a long extension to the wrench. Take off the plastic cover on the middle engine, to reveal the 4 plug lead tops. These need to be carefully prised clear to reveal the plugs below, deep in their housings. Unscrew each plug in turn, and the magnetic socket will lift it clear. Replace with a new plug, taking extra care so that the plug doesn't go in cross threaded.
John, July 2008
