Octane

Octane is the measure of a fuel's ability to resist a spark knock. A spark knock occurs in the combustion chamber just after the spark plug fires, when the air/fuel mixture in the cylinder does not completely burn. The remaining mixture spontaneously combusts due to temperature and pressure. This secondary explosion causes a vibration that is heard as a knock (ping). Fuel with a high octane number has a greater resistance to a spark knock. This vehicle requires 91 octane ([R+M]/2 method) in order to ensure the proper performance of the fuel control system. Using fuel with an octane rating lower than 91 can create a spark knock. This can cause poor engine performance and a reduction in fuel economy. Also, in severe knock cases, engine damage may occur.