1997 Ford Aerostar Owner's Manual - Page 264

Do not be concerned if your vehicle sometimes knocks lightly. However, if it knocks heavily under most driving conditions on the recommended octane fuel, see your dealer or a qualified service technician to prevent any engine damage. Fuel quality If you are experiencing starting, rough idle or hesitation problems, try a different brand of fuel. If the condition persists, see your dealer or a qualified service technician. The American Automobile Manufacturers Association (AAMA) issued a gasoline specification to provide information on high quality fuels that optimize the performance of your vehicle. We recommend the use of gasolines that meet the AAMA specification if they are available. It should not be necessary to add any aftermarket products to your fuel tank if you continue to use a high-quality fuel. Gasolines for clean air Ford approves the use of gasolines to improve air quality, including reformulated gasolines that contain oxygenates such as a maximum of 10% ethanol or 15% MTBE. There should be no more than 5% methanol with cosolvents and additives to protect the fuel system. Safety Information Relating to Automotive Fuels RWARNING Automotive fuels can cause serious injury or death if misused or mishandled. u Turn vehicle off when refueling. 265