Fuel Quality - Ford Ranger Owner's Manual

In some parts of the country, "premium" grade fuels are sold
with octane ratings of less than 91, especially in high altitude
areas. It is recommended that you use only those "premium"
fuels with an octane rating of 91 or higher.

Fuel Quality

If you are experiencing starting, rough idle or hesitation
problems when the engine is cold, it may be caused by fuel
with low volatility. Try a different brand of fuel. If the
condition persists, see your dealer or a qualified service
technician.
Using a high-quality fuel makes your vehicle more responsive
and maintains its good fuel economy and emissions by:
minimizing deposits in fuel injectors, combustion chambers
and on intake valves.
assuring quick starting and smooth warm-up.
protecting the fuel system from vapor lock in very hot
weather, which causes the engine to hesitate or stall and
makes restarts difficult.
protecting your fuel system from rusting.
preventing the fuel lines from freezing.
preventing the fuel system from "gumming up" when your
vehicle is not used for long periods of time.
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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