Many people have experienced an engine knocking or pinging during acceleration. This sound is created when fuel ignites prematurely. Anti-knock characteristics relate directly to octane ratings. The higher the octane rating the more the fuel resists knocking. It takes a higher temperature and more compression to ignite a fuel with a higher octane. Modern engines use knock sensors (KS), also known as detonation sensors, to identify when slight knocking begins to occur. When a sensor detects knocking (through engine vibrations), a signal is sent to the computer to retard the spark ignition timing until the knock is eliminated. This improves performance, reduces emissions, and avoids engine damage. Even though a knock isn’t audible to the ear, it may be occurring.