Ford 1997 Aspire Manual page 179

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 recommendation
Your vehicle is designed to use regular gasoline
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.
Typical octane rating label
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.
177