In a Waste-Spark DIS, how does one coil fire two spark plugs?

• A. All coils fire sequentially
• B. One coil fires two spark plugs at the same time when one cylinder is on the compression stroke, and the other cylinder is on the exhaust stroke (Correct)
• C. Each coil fires only one spark plug
• D. Two cylinders fire on opposite strokes

Answer: (B)

In a Waste-Spark DIS, a single ignition coil fires two spark plugs at the same moment. The two cylinders connected to that coil are at opposite points in their four-stroke cycle—when one is on the compression stroke and needs a spark to ignite the air-fuel mix, the other is on the exhaust stroke and doesn’t need a spark for combustion. So the coil produces a spark in both plugs at once, but only the compression-stroke cylinder benefits; the spark in the exhaust-stroke cylinder is wasted, hence the name “waste spark.” This arrangement reduces the number of coils and wiring while still delivering proper timing for the cylinders.