1996 Ford Mustang Owner's Manual - Page 238

Octane recommendations Your engine is designed to use fuel with an octane rating of 87. In most cases it is not necessary to use a fuel with an octane rating higher than 87. At service stations, the octane rating is displayed in a label on the pumps. Using a fuel with a lower octane rating can cause persistent and heavy knocking, which can damage the engine. Do not be concerned if your vehicle sometimes knocks lightly when you drive up a hill or when you accelerate. However, see your dealer or a qualified service technician if persistent heavy knocking occurs because this can damage the engine. If your vehicle has problems with starting, rough idle or hesitation problems when the engine is cold, it may be caused by fuel with low volatility. Try a different brand of fuel. If the condition persists, see your dealer or a qualified service technician. Gasolines for clean air Fuels in certain areas of the country are required to contain oxygenates to improve air quality. Common oxygenates are ethanol or grain alcohol (blended at no more than 10%), methanol or wood alcohol (blended at no more than 5% with cosolvents and additives), and MTBE or methyl tertiary butyl ether (blended at no more than 15%). 244