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Spark Plugs

The spark plug, used in all generations of ignition systems, completes the high voltage circuit. Spark plugs can be found at the end of spark plug wires or under coil packs on COP systems. Spark plugs are screwed into the engine head so their electrodes at the tip are exposed to the combustion chamber. Voltage at the spark plug needs to be great enough to arc across the gap between the electrodes. This spark is what ignites the air-fuel mixture. Most engines have one spark plug per cylinder, but some have two. The center electrode on a spark plug is commonly made of copper, platinum, or iridium. The gap between the center electrode and the ground electrode is usually between 0.020 to 0.080 of an inch (0.51 to 2.03 mm). Always check the service manual or the VECI sticker under the hood for the gap setting.