They are located in the engine head. Follow the spark plug wires down to the spark plugs. Most require a 5/8 or 11/16 deep well socket to remove them. Make sure it has a rubber grommet in the end of the socket so you do not break the porcelain of the spark plug.
Spark plugs are usually located at the top of the engine. They go into the cylinders and produce the spark at the correct time for the controlled explosion to happen in each cylinder. The design of each engine varies. The easiest way to find out where the spark plugs are would be to go to your technician and have them pointed out to you.
〉 Answered on Feb 26th, 2008 by Suzanne Grego, Technician at City of Philadelphia Fleet Management