Caution: Spark plug replacement at this service interval is required on HCS, Endura-E, CVH and PTE engines. On Zetec and Zetec-E engines, the recommended interval for replacing spark plugs is every 48,000 km or three years.
Before removing the spark plugs, remove any dirt using a clean brush, vacuum cleaner or compressed air to prevent dirt from entering the engine cylinders.
Remove the high-voltage wire tips from the spark plugs, and remove them by the tip, not the wire.
Remove the spark plugs. Checking the spark plugs indicates the condition of the engine. If the tip of the spark plug insulator is clean and white, this indicates that the mixture is too lean or "hot" spark plugs are being used.
If the tip and nose of the insulator are coated with a hard black film, this indicates that the mixture is too rich. If it is black and oily, the engine is probably worn.
If the nose of the insulator is covered with a light light brown coating, then the mixture is optimal and the engine is probably in good condition. Use a feeler gauge to check the spark plug gap (see Fig. 1.19, 1.20).
The spark plug gap is important because if the gap is too large or too small, the spark size and efficiency will be insufficient for normal engine operation.
To set the interelectrode gap, bend the outer electrode until the required gap is obtained. Do not bend the central electrode under any circumstances, as this may split the insulator.
Wipe the threaded part of the spark plug thoroughly.
Screw in the spark plug by hand, making sure it is not tilted until it touches the cylinder head, and tighten it to the required torque.
If a torque wrench is not available, tighten each spark plug no more than a quarter turn (CW and PTE engines) or a sixth turn (HCS and Endura-E engines).
The text was obtained in its entirety from the specified website (FORDBOOK)