FORD 2012 Focus v.5 - Manual (Page 357)

Do not be concerned if your engine sometimes knocks lightly. However, if
it knocks heavily under most driving conditions while you are using fuel
with the recommended octane rating, see your authorized dealer to
prevent any engine damage.
FFV engine (if equipped)
If your vehicle is flex fuel capable, it is designed to use Fuel Ethanol
(Ed75–Ed85), “Regular” unleaded gasoline or any mixture of the two
fuels.
Use of other fuels such as Fuel Methanol may cause powertrain
damage, a loss of vehicle performance, and your warranty may be
invalidated.
It is best not to alternate repeatedly between gasoline and E85. If you do
switch fuels, it is recommended that you add as much fuel as
possible—at least half a tank. Do not add less than five gallons (18.9L)
when refueling. You should drive the vehicle immediately after refueling
for at least 5 miles (8 km) to allow the vehicle to adapt to the change in
ethanol concentration.
If you exclusively use E85 fuel, it is recommended to fill the fuel tank
with regular unleaded gasoline at each scheduled oil change.
Fuel quality
Unleaded gasoline engines
If you experience starting, rough idle or hesitation driveability problems
during a cold start, try a different brand of “Regular” unleaded gasoline.
FFV engines
If you experience starting, rough idle or hesitation driveability problems
during a cold start, try a different brand of E85 fuel. If the driveability
problems continue, fill the vehicle with regular unleaded gasoline and
drive vehicle normally until gasoline is used. See your authorized dealer
if the problem persists.
Do not add aftermarket fuel additive products to your fuel tank. 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. These
products have not been approved for your engine and 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.
Many of the world’s automakers approved the World-Wide Fuel Charter
that recommends gasoline specifications to provide improved
Maintenance and Specifications
357
2012 Focus (foc)
Owners Guide, 5th Printing
USA (fus)