144 Auto Engine Performance and Driveability Copyright by Goodheart-Willcox Co., Inc. This chapter identifies the components of the ignition system. The condition of the ignition system is critical to good engine operation and vehicle driveability. If the igni- tion system has any type of defect, the engine will not run properly or may not operate. This chapter covers the igni- tion components, reviewing the operation of each subsys- tem. Before beginning this chapter, you may want to review the basic electricity and electronics material in Chapter 6. Ignition System The air-fuel mixture cannot do any useful work unless it is ignited. On diesel engines, ignition is accomplished by high pressure, which heats the air-fuel mixture in the engine cylinder to its ignition point. On a gasoline engine, the ignition system produces a high-voltage spark that ignites the compressed air-fuel mixture in the engine cylinder. The gasoline ignition system is composed of: • Primary circuit that creates the high voltage needed to create a spark at the spark plug. • Secondary circuit that distributes the high voltage to the correct spark plug at the correct time and creates the spark. The components used in the primary and secondary circuits of various types of ignition systems are shown in Figure 8-1. The primary circuit will be covered first. Since the mid 1970s, all ignition systems have used electronic components to create and time the spark. These systems are referred to as electronic ignition systems. They are capable of generating as much as 100,000 volts to create a spark. Some ignition systems fire the spark plugs more than once on the power stroke to increase power and reduce emissions. Warning: Ignition systems operate at very high voltages. A shock from the ignition system can injure or kill. Use extreme care when working with any ignition system. Primary Ignition Circuit The primary ignition circuit creates high voltage electricity from the 12 volts available from the battery and charging system. It handles battery voltage or, depending on the system, less than battery voltage. The primary ignition circuit consists of: • Ignition coil. • Ignition control module. • Triggering device. • Associated wiring. • Resistor, in some cases. Ignition Coils The ignition coil is a type of transformer. It is a device that converts electricity from low to high voltage. This voltage increase results from creating a magnetic field and then collapsing it. The ignition coil consists of two coils of wire, or windings, around a soft iron core. The primary windings are composed of a few turns of heavy wire. The secondary windings are composed of many turns of fine wire. The core is made of soft iron as it will not become per- manently magnetized, which would upset coil operation. To create high voltage, battery current passes through the primary windings. The turns of heavy wire allow high current flow. This current flow creates a magnetic field. When the current flow through the primary windings is stopped, the magnetic field collapses. As the field collapses through the primary windings, the voltage in the primary windings is increased to about 200 volts. This is called self- induction, since the voltage increase is created in the same windings that produced the magnetic field. As the magnetic field collapses through the secondary windings, electricity is created in the secondary windings. This is a very high voltage, from 60,000–100,000 volts, but a very low current. The very fine wire in the secondary wind- ings does not allow the energy from the collapsing magnetic field to develop high current. The difference in the number of wire turns between the primary and secondary wind- ings determines how much the voltage is increased in the secondary windings. This high-voltage current is delivered through the secondary circuit to the spark plugs. The current discharges across the plug gap to ignite the air-fuel mixture. Flat Coil. The flat coil consists of primary and second- ary windings surrounded by a square iron frame, Figure 8-2. The windings are coated with epoxy to preserve the insula- tion between the primary and secondary windings. Many flat coils are also encased in heavy plastic to further insulate the windings. The positive and negative primary terminals are attached to the side of the coil. Some coils have a third wire that serves as a ground. The secondary output is at the center of the coil. Variations of the flat coil are used on most engines, except for some coil-on-plug ignitions. Most flat coils are installed near the distributor, as in Figure 8-3. Some coils are installed under a plastic cover on top of the distributor cap. In this case, the coil is not sealed and output goes directly to the rotor. Waste Spark Ignition Coil. Coils used with waste spark ignition systems may be part of the control module assembly, Figure 8-4. There is one coil for every two cylin- ders. In some cases, these coils can be individually replaced. On other systems, the entire assembly must be replaced if one coil becomes defective. Coil-on-Plug Ignition Coil. In a coil-on-plug ignition system, there is one ignition coil for each spark plug. The coil assemblies used in these systems generally consist of a coil, an ignition module, and an integral spark plug boot. See Figure 8-5. This type of coil is often called a COP coil. Pencil Coil. On some newer engines, the COP coil core is magnetized to allow a smaller coil size that produces