Figure 11 Typical spark plug problems showing damage which may indicate engine problems.

Figure 11 Typical spark plug problems showing damage which may indicate engine problems.

Tracking Arc: High-voltage arcs between a fouling deposit on the insulator lip and spark plug shell. This ignites the fuel/air mixture at some point along the insulator tip, retarding the ignition timing, which causes a power and fuel loss.

Tracking Arc & Wide Gap

Wide Gap: Spark plug electrodes are worn so that the high-voltage charge cannot arc across the electrodes. Improper gapping of electrodes on new or cleaned spark plugs could cause a similar condition. Fuel remains unburned and power loss results.

Flashover: A damaged spark plug boot, along with dirt and moisture, could permit the high-voltage charge to short over the insulator to the spark plug shell or the engine. A buttress insulator design helps prevent high-voltage flashover.

Flashover & Fouled Spark Plugs

Fouled Spark Plug: Deposits that have formed on the insulator tip may become conductive and provide a “shunt” path to the shell. This prevents the high voltage from arcing between the electrodes. A power and fuel loss is the result.

Bridged Electrodes: Fouling deposits between the electrodes “ground out” the high voltage needed to fire the spark plug. The arc between the electrodes does not occur and the fuel air mixture is not ignited. This causes a power loss and exhausting of raw fuel.

Bridged Electrode & Cracked Insulator Plugs

Cracked Insulator A crack in the spark plug insulator could cause the high voltage charge to “ground out.” Here the spark does not jump the electrode gap and the fuel air mixture is not ignited. This causes a power loss and raw fuel is exhausted.

*Figure 11* Typical spark plug problems showing damage which may indicate engine problems.
Tracking Arc: High-voltage arcs between a fouling deposit on the insulator lip and spark plug shell. This ignites the fuel/air mixture at some point along the insulator tip, retarding the ignition timing, which causes a power and fuel loss.		Wide Gap: Spark plug electrodes are worn so that the high-voltage charge cannot arc across the electrodes. Improper gapping of electrodes on new or cleaned spark plugs could cause a similar condition. Fuel remains unburned and power loss results.
Flashover: A damaged spark plug boot, along with dirt and moisture, could permit the high-voltage charge to short over the insulator to the spark plug shell or the engine. A buttress insulator design helps prevent high-voltage flashover.		Fouled Spark Plug: Deposits that have formed on the insulator tip may become conductive and provide a “shunt” path to the shell. This prevents the high voltage from arcing between the electrodes. A power and fuel loss is the result.
Bridged Electrodes: Fouling deposits between the electrodes “ground out” the high voltage needed to fire the spark plug. The arc between the electrodes does not occur and the fuel air mixture is not ignited. This causes a power loss and exhausting of raw fuel.		Cracked Insulator A crack in the spark plug insulator could cause the high voltage charge to “ground out.” Here the spark does not jump the electrode gap and the fuel air mixture is not ignited. This causes a power loss and raw fuel is exhausted.