2. SPARK PLUGS

3. PURPOSE Ignite the air fuel mixture in the cylinder to produce power. Ignite the air fuel mixture in the cylinder to produce power.

6. CONSTRUCTION Centre copper electrode inside a ceramic insulator, with a steel hexagon shaped shell. Centre copper electrode inside a ceramic insulator, with a steel hexagon shaped shell.

8. LOCATION Screwed into the cylinder head. Screwed into the cylinder head. Centre electrode extends into the combustion chamber. Centre electrode extends into the combustion chamber. Some spark plugs are easy to access and remove while some are not. Some spark plugs are easy to access and remove while some are not.

9. PROBLEMS Spark plugs wear from high mileage. Spark plugs wear from high mileage. The ceramic insulator may crack, allowing the spark to travel directly to ground, causing poor performance and fuel economy. The ceramic insulator may crack, allowing the spark to travel directly to ground, causing poor performance and fuel economy. Oil entering the cylinder or too much fuel, can cause the plug to foul, causing poor performance. Oil entering the cylinder or too much fuel, can cause the plug to foul, causing poor performance. Neglected spark plugs can seize in the threaded hole and break when trying to remove them. Neglected spark plugs can seize in the threaded hole and break when trying to remove them.

10. DIAGNOSIS Poor spark plug operation usually results in the engine running rough. Poor spark plug operation usually results in the engine running rough. Using an engine scope, observe the spark plug firing patterns. Using an engine scope, observe the spark plug firing patterns. Remove all spark plugs and visually inspect the spark plug centre electrode gap. Remove all spark plugs and visually inspect the spark plug centre electrode gap. Worn or defective spark plugs should be replaced as a set. Worn or defective spark plugs should be replaced as a set.

13. APPROXIMATE COST OF REPAIR Depending on quality and design of spark plug desired, prices range from $3 to $30 each. Depending on quality and design of spark plug desired, prices range from $3 to $30 each. Modern engines have 4, 6, 8, 10, or 12 cylinders. Each cylinder requires at least one spark plug. Modern engines have 4, 6, 8, 10, or 12 cylinders. Each cylinder requires at least one spark plug. Depending on vehicle design, labour to replace spark plugs can range from ½ hour on some 4 cylinder engines to over 3 or 4 hours for some more complex V8, V10 and V12 engines. Depending on vehicle design, labour to replace spark plugs can range from ½ hour on some 4 cylinder engines to over 3 or 4 hours for some more complex V8, V10 and V12 engines. Spark plugs are usually replaced during a ‘tune-up’. Spark plugs are usually replaced during a ‘tune-up’. Spark plugs MUST be properly ‘gapped’ when replacing them. Spark plugs MUST be properly ‘gapped’ when replacing them.