General information
The ignition system of the gasoline engine is integrated with the fuel injection system and is controlled by a single electronic control unit ECM (see Chapter Power and exhaust systems). The ignition system consists of the engine control module (ECM), ignition switch, ignition module (ICM) with integrated coils, spark plugs, high-tension wires and a set of information sensors.
All models discussed in this manual use a direct ignition system (without distributor).
On 1.6L SOHC and 2.0L DOHC engines the ignition module consists of an ignition coil and is equipped with four terminals. In fact, two separate ignition coils are mounted in the module, each of which, in response to commands from the ECM, supplies high voltage simultaneously to two spark plugs (1 and 4, 2 and 3). Ignition is organized according to the "idle spark" principle, that is, each spark plug produces a spark twice during the piston's working cycle - at the end of the compression stroke and at the end of the exhaust stroke. Since the mixture is not supplied to the combustion chamber during the exhaust stroke, no ignition occurs in it, despite spark formation, from which the principle got its name.
On 1.4, 1.6 and 1.8 L DOHC engines the ignition module includes four coils, one per cylinder. The coils are placed in a common housing, installed above the spark plugs. The design of the module eliminates the need for high-voltage wires, since the coils are connected directly to the spark plugs. ECM, based on the analysis of data received from the information sensors, in accordance with the program of the built-in processor, sends control electrical pulses to the ignition module, the configuration of which uniquely determines the moment of ignition.
The ignition timing angle is set and adjusted by the control module.
The ECM supplies control voltage to the primary windings of the ignition coils, inducing a magnetic field in them. The voltage supply is periodically interrupted, which leads to the disappearance of the field and, as a result, the generation of high-voltage voltage in the secondary winding. High-voltage voltage is supplied to the spark plugs. The interelectrode gap of the spark plugs is set so that when voltage is supplied to the plug, a "breakdown" occurs between the electrodes accompanied by sparking. The spark resulting from the "breakdown" ensures ignition of the air-fuel mixture. The moment of supplying a pulse to the plug is calculated by the control module based on an analysis of data received from information sensors on the current engine speed, the position of the crankshaft and camshafts, the amount of air supplied to the combustion chambers, etc. In addition to those listed, the factors affecting the functioning of the ignition system include the position of the throttle valve, engine temperature and detonation of the mixture. The corresponding information sensors are responsible for supplying the control module with the necessary information. The information received from the sensors is used not only to determine the exact time of the supply of explosive pulses to the spark plugs, but also to make operational adjustments to the mixture quality. A description of the procedures for removing and installing the sensors is given in Chapter Power and exhaust systems.
Engine speed and crankshaft position are determined by the control module based on information from the crankshaft position (CKP) sensor. The inductive head of the sensor is located near the toothed rotor on the flywheel. When a tooth passes the head, the sensor sends a voltage pulse to the ECM. One tooth on the flywheel is missing, its position corresponds to the position 90° before TDC of the piston of the first cylinder. At this moment, the sensor gives a gap, allowing the module to monitor the position of the crankshaft. The camshaft position (CMP) sensor informs the control module which of the pistons is at the end of the compression stroke.
Engine load information is supplied to the ECM from the air mass sensor (mAF sensor) and the throttle position sensor (TPS). The load level is determined by the amount of air sucked into the engine, and is adjusted based on information from the knock sensor (KS). The knock sensor is installed on the cylinder block and informs the ECM about premature detonation ignition of the mixture in the cylinders that occurs with increasing load. The sensor recognizes the moment of detonation onset by an increase in the vibration background caused by knocking in the cylinders. Upon receiving information from the sensor about the occurrence of detonation of the air-fuel mixture, the ECM delays the ignition control pulse, reducing the advance until the moment of detonation stops.
Sensors for engine temperature, throttle position, vehicle speed, automatic transmission selector position and air conditioning activation (depending on the configuration) transmit additional information to the ECM about the current state of the corresponding vehicle components and assemblies. Based on the analysis of continuously changing input information, the control module adjusts the ignition timing, injection timing, and air-fuel mixture quality.
If any of the sensors fail to generate signals, the ECM switches to emergency operation mode and begins to use the basic settings stored in the processor memory, allowing the vehicle to be driven under its own power to a parking place or a service station. The engine's output efficiency may be significantly reduced due to the cessation of continuous adjustment of operating parameters, while fuel consumption, on the contrary, may increase. When the on-board self-diagnostic system detects a malfunction, it enters a corresponding fault code into the module's memory (see Chapter Engine electrical equipment).
It should be remembered that a complete diagnosis of the engine management system can only be performed using special diagnostic equipment that allows reading the failure codes stored in the processor memory. Analysis of the read information allows you to quickly identify the source of the failure and eliminate the cause of its occurrence.
Precautionary measures
The electronic ignition system generates very high voltage! Be careful and take all necessary precautions when servicing any components of the system, including not only the main (ignition module, coil and high voltage wires), but also related items such as spark plug connectors, tachometer and other equipment. Persons with an implanted pacemaker should not be allowed to service ignition system components!
To avoid damage to ignition system components and to reduce the risk of personal injury, observe the following precautions.
- If the engine does not start, do not keep the ignition on for more than 10 seconds.
- Before disconnecting any system component wiring, turn off the ignition.
- Before connecting and disconnecting diagnostic equipment (for example, a strobe) turn off the ignition
- Do not allow the ignition coil windings to be grounded.
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