1998 Ford Escort Owner's Manual - Page 157

Maintenance and care Your vehicle was not designed to use fuel or fuel additives with metallic compounds, including manganese-based compounds containing MMT. Vehicles certified to California emission standards (indicated on the underhood Vehicle Emissions Control Information label) are designed to operate on California reformulated gasolines. If California reformulated gasoline is not available when you refuel, your vehicle can be operated on non-California fuels. However, even though your engine will perform adequately on other gasolines, the performance of the emission control devices and systems may be adversely affected. Repair of damage caused by using a fuel that your vehicle was not designed for may not be covered by your warranty. Octane recommendations Your vehicle is designed to use regular unleaded with an (R+M)/2 octane rating of 87. We do not recommend gasolines labeled as "regular" in high altitude areas that are sold with octane ratings of 86 or even less. Do not be concerned if your vehicle sometimes knocks lightly. However, if it knocks heavily under most driving conditions on fuel with the recommended octane, see your dealer or a qualified service 87 157