Ford 1997 Aerostar 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
Automotive fuels can cause serious injury
or death if misused or mishandled.
Turn vehicle off when refueling.
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