increased fuel consumption, loss of engine power, reduced maximum vehicle speed, hard starting, and other signs of abnormal operation.

GENERAL INFORMATION.

Worn or dirty spark plugs may run acceptably at engine idle, but their operation deteriorates as engine speed increases.

Signs of poor spark plug operation include

increased fuel consumption, loss of engine power, reduced maximum vehicle speed, hard starting, and other signs of abnormal operation.

of the engine. Spark plugs may fail due to heavy carbon deposits, incorrect electrode gap, or insulator damage..

Spark plug fouling caused by heavy carbon deposits occurs when the engine operates at low speeds for long periods and during frequent short trips,.

when the engine usually does not have time to warm up to normal operating temperature..

Carbon deposits are promoted by worn piston rings and poor operation of the

ignition system, an overly rich fuel mixture, and an incorrect spark plug heat range (plugs that are too "cold" for the given engine). An increase in the

electrode gap after a short mileage indicates that the engine is operated under heavy-duty conditions or that the spark plugs have an incorrect heat range (plugs that are too "hot" for the given engine). Electrode wear

may also be the result of plug overheating due to hot gas leakage through the

thread seal (plug not tightened sufficiently). A lean fuel mixture also

promotes electrode wear. Insulator damage may result from

incorrect plug installation or careless handling during

electrode gap adjustment, as well as from dropping or impact. An insulator crack

may not appear immediately; it becomes noticeable after some time when

dirt gets into it. Usually the insulator cracks under the plug shell, and the crack cannot be seen.