FORD 2003 Mustang v.3 - Manual (Page 179)

Mach 1
Your vehicle is
designed to use
“Premium” unleaded
gasoline with an
(R+M)/2 octane rating of 91 or higher for optimum
performance. The use of gasolines with lower octane
ratings may degrade performance. We do not
recommend the use of gasolines labeled as
“Premium” in high altitude areas that are sold with
octane ratings of less than 91.
If your engine knocks under most driving conditions
while you are using fuel with the recommended
octane rating, see your dealer or a qualified service
technician to prevent any engine damage.
Fuel quality
If you are experiencing starting, rough idle or
hesitation driveability problems during a cold start,
try a different brand of “Regular” unleaded gasoline.
“Premium” unleaded gasoline is not recommended
(particularly in the United States) because it may
cause these problems to become more pronounced.
If the problems persist, 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
high quality fuel of the recommended octane rating.
Aftermarket products could cause damage to the
fuel system. Repairs to correct the effects of using
an aftermarket product in your fuel may not be
covered by your warranty.
91
(R+M)/2 METHOD
Maintenance and Specifications
179