Operation

In this EI system there is one coil for each pair of cylinders. Each pair is at Top Dead Center (TDC) at the same time, and are known as companion cylinders. The cylinder that is at TDC of its compression stroke is called the event cylinder. The cylinder that is at TDC of its exhaust stroke is called the waste cylinder. When the coil is triggered both plugs fire at the same time, completing a series circuit. Because the lower pressure inside the waste cylinder offers very little resistance the event cylinder uses most of the available voltage producing a very high energy spark. This is known as waste spark ignition.