5.2 Spark Plugs

High temperature and high voltage sparks eventually wear out the spark plug electrodes, and the spark plugs must be replaced. To replace a spark plug, gently remove the spark plug wire by pulling on the protective boot, and blow or brush away any dirt from around the base of the plug to prevent it from entering the engine when the plug is removed.

Use a 13/16 in. spark plug socket to remove spark plugs on all except 16-valve engines. On 16-valve engines, use a 5/8 in. spark plug wrench with a rubber insert that will hold the plugs for installation and removal in the deep spark plug recesses.

The correct spark plugs for the different engines covered by this manual are listed in Table h. Use a spark plug gap gauge to check the gap. If necessary, bend the outer electrode slightly to adjust the gap to meet the specification. Do not bend or file the center electrode.

Table h. Spark Plug Specifications

Lightly lubricate the new spark plug threads with a little oil or grease, and thread the plugs in the engine by hand, to prevent cross-threading. Torque the spark plugs to no more than 20 Nm (15 ft. lb.).

For California models, it is recommended for emission control that the spark plugs be removed and cleaned every 15,000 miles (24,000 km). Checking the plugs at this interval on all models can be informative, as the condition of the spark plug is a good indicator of combustion quality which can help diagnose engine faults. Fig. 5-4 shows some examples of spark plug condition and what they mean.

Clean lightly-fouled spark plugs with a light wire brush, and remove all debris from around the electrode. Do not chip the ceramic insulator. Badly fouled spark plugs should be replaced, and the cause of the fouling should be investigated and corrected.

Fig. 5-4.

Spark plug appearance which may indicate engine condition. For more information on interpreting spark plug condition, see ENGINE. Photos courtesy of Champion Spark Plug Co.