Copyright Goodheart-Willcox Co., Inc. Chapter 10 ∣ Ignition Systems 209 A distributorless ignition creates a high-voltage spark using multiple ignition coils. Multiple coils must be used since there is no distributor cap and rotor to distribute the spark. There are several types of distributorless ignition systems, including waste spark systems, coil-near-plug systems, and coil-on-plug systems. Waste Spark Ignition System In a waste spark ignition system, there is one ignition coil for every two cylinders. In this type of system, a four-cylinder engine has two coils, a six cylinder has three coils, and a V-8 has four coils. The coils are often mounted together in a coil pack, Figure 10-10. Each coil in a waste spark system has two discharge terminals. These terminals are connected to two spark plugs through conventional resistor secondary wires. When the coil fires, the spark exits one terminal, travels through the plug wire to fire the plug, and returns to the other coil terminal through the engine block, the other spark plug, and the other spark plug wire. In effect, the coil fires both plugs at the same time. The coil wires are arranged so the coil fires one plug in a cylinder that is on the top of the compression stroke and the other plug in a cylinder that is on the top of the exhaust stroke. The plug firing on the top of the exhaust stroke has no effect on the operation of the engine. Therefore, the arc at this plug is referred to as a waste spark. Since it takes very little voltage to jump the spark plug gap on the exhaust stroke, the coil is powerful enough to fire both plugs. Coil-Near-Plug Systems Some distributorless ignition systems use one coil for each spark plug. These systems, com- monly called a coil-near-plug ignition system, use a short secondary wire to connect each coil to its respective plug. See Figure 10-11. Coil-on-Plug System Many late-model engines are equipped with a coil-on-plug (COP) ignition system, or a direct ignition system. These systems do not use secondary (spark plug) wires or conductor strips. Instead, the coil assemblies are installed directly over the spark plugs, Figure 10-12A. There is one coil assembly for every spark plug. Each coil assembly consists of a coil, a module, and a spark plug boot, Figure 10-12B. The spark plug boot prevents arcing and keeps water from entering the coil-to-plug connection. Goodheart-Willcox Publisher Figure 10-10. The coils in a waste spark ignition are often part of a coil pack, such as the one shown here. This particular coil pack is for a 6-cylinder engine. Each coil fires two spark plugs. Ignition coils Secondary wires Goodheart-Willcox Publisher Figure 10-11. This distributorless ignition system uses one coil per cylinder. Note the short secondary wires, which connect the coils to the spark plugs.