Ignition Coil: Description and Operation

IGNITION COILS

Spark distribution is achieved by a pack of coils mounted at the rear of the engine compartment. Coil operation is controlled by the ECM. A single coil is used to fire two plugs simultaneously - one on the compression stroke and the other on the exhaust stroke. The circuit for each coil is completed by switching within the ECM.

The spark on the exhaust stroke is said to be wasted hence, the term "wasted" or "lost" spark ignition system. Actually, little in the way of voltage is wasted on the spark in the cylinder on the exhaust stroke. The cylinder containing the air/fuel mixture (compression stroke) conducts the electrical charge far more efficiently than the cylinder containing exhaust gasses. Most of the voltage takes this path of least resistance to ground.

Performance is also improved. By using more than one coil (as opposed to the traditional single coil system) each coil is allowed more time to charge between firings.