General Information on the Ignition System

The ignition system is part of the integrated engine control system. The design details of ignition systems differ among engine types, but the operating principle is the same.

The integrated ignition systems (IIA) installed on the 4A-FE engine include a distributor (Fig. 6.1.1.) with two rotors, pickup coils, an ignition coil, a capacitor, and an electronic ignition switch.

Fig. 6.1.1. General view of the distributor with spark plug high-tension leads.

In the ignition systems of 4A-FE engines operating on a lean mixture, the ignition coil and electronic ignition switch are located separately, and the distributor includes two rotors and pickup coils.

On 3S-FE engines the ignition system has two rotors, pickup coils and an ignition coil in the distributor, while the igniter is installed separately in the engine compartment.

In all systems, all components are connected to the Engine Control Module (ECM). The sensors installed in the distributor housing generate signals that indicate rotation angles: the NE sensor for the crankshaft and the G sensor for the camshaft.

The electronic engine control system is programmed to provide the required ignition timing under all engine operating conditions. The ECM receives information from the engine speed and engine coolant temperature sensors, the mass air flow or volume air flow sensor, and based on this data determines the optimum ignition timing and sends a signal to the igniter at the proper moment. The igniter switches the primary winding of the ignition coil on and off. As a result, a high voltage current is induced in the secondary winding, which is delivered through the distributor and high-tension cables to the spark plug of the cylinder firing next.

Safety Precautions. · Do not leave the ignition switch on for more than 10 minutes with the engine stopped.

· If a separate tachometer is required for any checks, first consult a specialist familiar with Toyota ignition systems: some types of tachometers may be incompatible with certain systems. When connecting a tachometer, follow the manufacturer's instructions. · Never connect the ignition coil terminals to ground: this may damage the coil or the Engine Control Module (ECM).

· Do not disconnect the battery while the engine is running.