1998 Ford Crown Victoria Owner's Manual - Page 133

Maintenance and care Octane recommendations Your vehicle is designed to use "Regular" unleaded gasoline with an (R+M)/2 octane rating of 87. We do not recommend gasolines labeled as (R+M)/2 METHOD "Regular" that are sold with octane ratings of 86 or lower in high altitude areas. Do not be concerned if your engine sometimes knocks lightly. However, if it knocks heavily under most driving conditions while you are using fuel with the recommended octane rating, see your dealer or a qualified service technician to prevent any engine damage. 87 Fuel quality If you are experiencing starting, rough idle or hesitation driveability problems during a cold start, try a different brand of "Regular" unleaded gasoline. "Premium" unleaded gasoline is not recommended (particularly in the United States) because it may cause these problems to become more pronounced. If the problems persist, see your dealer or a qualified service technician. The American Automobile Manufacturers Association (AAMA) issued a fuel specification to provide information on high quality fuels that optimize the performance of your vehicle. We recommend the use of fuels 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. Cleaner air Ford approves the use of gasolines to improve air quality, including reformulated gasolines that contain oxygenates up to 10% ethanol or 15% MTBE. Do not use gasolines containing methanol, which can damage critical fuel system components. Damage resulting from the use of methanol may not be covered by your warranty. 133