Ford 1999 Wagon-Econoline Owner's Manual page 172

Maintenance and care
Octane recommendations
Your vehicle is designed to use
87
"Regular" unleaded gasoline with an
(R+M)/2 octane rating of 87. We do
not recommend the use of gasolines
(R+M)/2 METHOD
labeled as "Regular" that are sold
with octane ratings of 86 or lower in high altitude areas.
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 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.
The American Automobile Manufacturers Association (AAMA) issued a
fuel specification to provide information on high quality fuels that
optimize the performance of your vehicle. We recommend the use of
fuels that meet the AAMA specification if they are available.
It should not be necessary to add any aftermarket products to your fuel
tank if you continue to use a high-quality fuel.
Cleaner air
Ford approves the use of gasolines to improve air quality, including
reformulated gasolines that contain oxygenates up to 10% ethanol or
15% MTBE.
Running out of fuel
Avoid running out fuel because this situation may have an adverse affect
on modern powertrain components.
If you have run out of fuel:
• You may need to crank the engine several times before the system
starts to pump fuel from the tank to the engine.
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