It would be better to know which car but here's how to proceed in general
- The night before you change the plugs, while the motor is still hoat, soak the seats where the plugs are screwed in with rust dissolver (caramba, MoS2).
- Next day, warm up the motor (not too hot), i.e. a few kms
- remove the cable plugs (same manufacturers have a real tricky system). that fancy plyers which remove the insulation of a cable usually do a good job!
- remove all dust and dirt with a small brush. you dont want any of that trash falling in...
- again, spray some rust dissolver so it penetrates into the thread and let it sink in for like 10 min's.
- unscrew the plugs carefully and slowly. if they brake, you're in trouble.
- screw in the new plugs. careful! a torque of 10NM should do.
good luck
Uwe
October 2007