Motorola Radius PM400

18
Chapter 8
Operation of a Conventional Ignition System
8.1 Introduction
To effectively reduce ignition interference in a vehicle, it is necessary to understand the operation of
an automobile ignition system.
Ignition is necessary in a gasoline engine to ignite the gasoline vapor and the air mixture in its
cylinders. The system is made up of the battery, distributor, breaker points, coil, condenser, and spark
plugs. The battery is the only electrical source of power in an automobile, so the lower battery voltage
must be stepped up to the high voltage necessary to arc across the spark plug electrodes. This arc
ignites the gas mixture.
8.2 Sources of Ignition Interference
In the conventional ignition system (Figure 8-1) a mechanical circuit breaker (the cam and points in
the distributor) opens the primary circuit of the ignition coil, and high voltage is developed at the
secondary. This high voltage is synchronized and applied to each spark plug by the distributor.
Figure 8-1. Typical Vehicular Ignition System, Simplified Schematic Diagram
HV Lead
Distributor
Spark plug leads
Spark
Plugs
Ignition
Coil
Condenser
Cam
Breaker
Points
Ignition
Switch
Battery
Ignition
Coil
Condenser
Stray
Capacitance
Cam
Breaker
Points
Ignition
Switch
Battery
Rotor Gap
Lead Inductance
Spark Plug Gap
FL0830261-O