1996 Ford F150 Owner's Manual - Page 313

Do not be concerned if your vehicle sometimes knocks lightly when you drive up a hill or when you accelerate. However, if a fuel with the recommended octane rating knocks heavily under all driving conditions or knocks lightly driving at cruising speed on level roads, see your dealer or a qualified service technician. Persistent, heavy knocking can damage the engine. 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: u protecting your fuel system from rusting. u preventing the fuel lines from freezing. u improving vehicle starting and warm-up. u protecting the fuel system from vapor lock in very hot weather, which causes the engine to hesitate or stall and makes restarts difficult. combustion chambers, and on intake valves. up" when your vehicle is not used for long periods of time. pinging. u minimizing deposits in fuel injectors, u preventing your fuel system from "gumming u preventing your engine from knocking and It should not be necessary to add any aftermarket products to your fuel tank if you continue to use a high-quality fuel. 314