1996 Ford Crown Victoria Owner's Manual - Page 257

Octane recommendations Your engine is designed to use fuel with an octane rating of 87. In most cases it is not necessary to use a fuel with an octane rating higher than 87. At service stations, the octane rating is displayed in a label on the pumps. Using a fuel with a lower octane rating can cause persistent and heavy knocking, which can damage the engine. Do not be concerned if your vehicle sometimes knocks lightly when you drive up a hill or when you accelerate. However, see your dealer or a qualified service technician if persistent heavy knocking occurs because this can damage the engine. If your vehicle has problems with 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. 241