Ford 1996 Taurus 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 rating fuel, see your dealer
or a qualified service technician to prevent any
engine damage.
SHO 3.4L engine
The SHO 3.4L engine has been designed to
operate using premium unleaded fuel with an
octane rating of 91 or higher. Regular unleaded
fuel with an octane rating of 87 may be used if
necessary. For optimum performance and
driveability, it is recommended that you use
premium unleaded fuel.
In some high altitude areas, "premium" fuels are
sold with octane ratings of less than 91. It is
recommended that you use only those
"premium" fuels with an octane rating of 91 or
higher.
Fuel quality
Ford approves the use of gasolines, including
those reformulated, that contain oxygenates such
as ethanol (10% maximum) and MTBE (15%
maximum). If methanol is used, the gasoline
should contain no more than 5% with
cosolvents.
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.
It should not be necessary to add any
aftermarket products to your fuel tank if you
continue to use a high-quality fuel.
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