Spark Plug: Description and Operation

SPARK PLUGS
All engines use resistor type spark plugs. Remove the spark plugs and examine them for burned electrodes and fouled, cracked or broken porcelain insulators. Keep plugs arranged in the order in which they were removed from the engine. A single plug displaying an abnormal condition indicates that a problem exists in the corresponding cylinder. Replace spark plugs at the intervals recommended in Lubrication and Maintenance

Spark plugs that have low milage may be cleaned and reused if not otherwise defective, carbon or oil fouled.