Copyright Goodheart-Willcox Co., Inc. 201 Chapter 10 Ignition Systems Objectives After studying this chapter, you will be able to: ✓ Explain why battery voltage must be increased in the ignition system. ✓ Describe the primary circuit of an ignition system. ✓ Describe the secondary circuit of an ignition system. ✓ Summarize the basic function and operating principles of ignition system components. ✓ Explain how various types of electronic distributorless ignition systems operate. ✓ Explain the concept of ignition timing. C hapters 4, 5, and 6 made frequent ref- erence to the use of a spark to ignite the air-fuel mixture. This chapter will provide you with a clear and concise descrip- tion of the various units in the ignition system. The theory, design, and construction of the parts will be discussed. You will also learn how they are combined to produce, control, and distrib- ute the spark. Before beginning this chapter, be sure that you are familiar with the material in Chapter 8, Electrical System Fundamentals. This will provide you with a basic introduction to electricity and electronics. Such knowledge is essential to understanding ignition systems. High Voltage Is Necessary Jumping a spark plug gap requires thousands of volts. However, the vehicle electrical system produces a maximum of about 14.5 volts and may drop below 12 volts when the engine is being cranked. Since this is not enough voltage to jump across the electrodes of a spark plug, a way to raise the voltage is needed. In modern vehicles, the voltage needed at the spark plugs can exceed 100,000 volts. This means that the original 12–14.5 volts is increased many times. The ignition system is divided into two separate circuits: the primary circuit and the secondary circuit. Since the mid 1970s, all vehi- cle ignition systems have used electronic components to create and time the spark. These systems are called electronic ignition systems. The components used in the primary and secondary circuits of various types of electronic ignition systems are shown in Figure 10-1. The primary circuit will be covered first. Primary Circuit The primary circuit consists of the battery, ignition switch, resistor (old distributor systems), ignition control module, and the ignition coil’s primary windings. These parts will be covered in the order that electricity flows through them. The primary circuit voltage is low, ranging from 12–14.5 volts. The wiring in this circuit is covered with a thin layer of insulation to prevent short circuits. Battery To better understand the operation of the ignition system’s primary circuits, we will start at the battery and trace the flow of electricity through the system. The battery is the source of electrical energy needed to operate the ignition system. It stores and produces electricity through chemical action. When the battery is being charged, it con- verts electricity into chemical energy. When the battery is discharg- ing (producing current), it converts chemical energy into electricity.