Octane Recommendations; Unleaded Gasoline Engines; Ffv Engine - Ford 1999 Ranger Owner's Manual

Maintenance and care
Do not use fuel containing methanol. It can damage critical fuel systems
components.
Vehicles certified to meet California emission standards (indicated on the
underhood Vehicle Emissions Control Information label) are designed to
operate on California cleaner-burning, low-sulfur gasolines. If you have a
California-certified vehicle and California cleaner—burning gasoline is not
available when you refuel, your engine should perform adequately.
However, the performance of the emission control devices and systems
may be adversely affected. In New York and Massachusetts, which have
adopted California's emission standards without requiring the sale of
California cleaner-burning gasoline, repairs to correct the effects of using
non-California fuel may not be covered by the emissions warranty.
Your vehicle was not designed to use fuel or fuel additives with metallic
compounds, including manganese-based compounds containing (MMT).
Repairs to correct the effects of using a fuel for which your vehicle was
not designed may not be covered by your warranty.

Octane recommendations

Do not be concerned if your engine
87
sometimes knocks lightly. However,
if it knocks heavily under most
driving conditions while you are
(R+M)/2 METHOD
using fuel with the recommended
octane rating, see your dealer or a qualified service technician to prevent
any engine damage.

Unleaded Gasoline engines

Your vehicle is designed to use "Regular" unleaded gasoline with an
(R+M)/2 octane rating of 87. We do not recommend the use of gasolines
labeled as "Regular" that are sold with octane ratings of 86 or lower in
high altitude areas.

FFV engine

Your vehicle is designed to use Fuel Ethanol (E85), "Regular" unleaded
gasoline or any percentage of the two fuels combined.
U.S. government regulations require fuel ethanol dispensing
pumps to have a small, square, orange and black label with the
common abbreviation E85 or the appropriate percentage for that
region. Use of other fuels such as Fuel Methanol may cause
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