General information
The ignition system of the gasoline engine is integrated with the fuel injection system and controlled by a single ECM (see chapter Power and exhaust systems). The ignition system consists of an engine control module (ECM), ignition switch, ignition module (ICM) with built-in coils, spark plugs, high-voltage wires and a set of information sensors.
All models covered in this manual use a direct type ignition system (without distributor).
On engines 1.6 l SOHC and 2.0 l DOHC 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, according to the commands coming from the ECM, supplies HV voltage simultaneously to two spark plugs (1 and 4, 2 and 3). Ignition is organized according to the principle «idle spark», that is, each candle gives out a spark twice per piston 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 sparking, from which the principle gets its name.
On engines 1.4, 1.6 and 1.8 l DOHC The ignition module has four coils, one per cylinder. The coils are placed in a common housing mounted 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 information coming from information sensors, in accordance with the program of the built-in processor, issues control electrical impulses to the ignition module, the configuration of which uniquely determines the ignition moment.
The ignition timing is set and adjusted by the control module.
The ECM applies 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 is applied to the spark plugs. The interelectrode gap of the spark plugs is set in such a way that when voltage is applied to the spark plug, sparking occurs between the electrodes «breakdown». The resulting «breakdown» a spark that ignites the air-fuel mixture. The moment the impulse is applied to the spark plug is calculated by the control module based on the analysis of data received from information sensors on the current engine speed, the position of the crankshaft and camshaft, the amount of air supplied to the combustion chambers, etc. In addition to the above, the factors that affect the operation of the ignition system include throttle position, engine temperature and mixture knock. The appropriate information sensors are responsible for supplying the necessary information to the control module. The information coming from the sensors is used not only to determine the exact time of applying explosive pulses to the spark plugs, but also to make operational adjustments to the quality of the mixture. A description of the procedures for removing and installing sensors is given in Chapter Power and exhaust systems.
Engine speed and crankshaft position are determined by the control module based on the analysis of information from the crankshaft position sensor (CKP). The inductive sensor head is placed close to the toothed rotor on the flywheel. As the 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 of 90°before TDC of the piston of the first cylinder. At this point, the sensor gives a pass allowing the module to track the position of the crankshaft. Camshaft position sensor (CMP) informs the control unit which piston is at the end of the compression stroke.
Engine load information is sent to the ECM from the air mass meter (MAF sensor) and throttle position sensor (TPS). The load level is determined by the amount of air sucked into the engine, and is corrected based on information from the knock sensor (KS). The knock sensor is mounted on the cylinder block and informs the ECM of pre-ignition of the mixture in the cylinders that occurs with increasing load. The sensor recognizes the start of detonation by increasing the vibration background caused by knocking in the cylinders. Upon receiving information from the sensor that knocking has occurred in the air-fuel mixture, the ECM delays the ignition control pulse, reducing the lead until the knock stops.
Sensors for engine temperature, throttle position, vehicle speed, automatic transmission selector position and air conditioning activation (depending on configuration) transmit additional information to the ECM about the current state of the relevant components and assemblies of the vehicle. Based on the analysis of continuously changing input information, the control module adjusts the ignition timing, injection timing, and the quality of the air-fuel mixture.
In the event of a malfunction in the generation of signals from any of the sensors, the ECM switches to emergency operation mode and begins to be guided by the basic settings stored in the processor's memory, which allow you to drive the car on its own to a parking lot or to a service station. In this case, the efficiency of the engine recoil can be significantly reduced due to the cessation of continuous adjustment of operating parameters, and fuel consumption, on the contrary, can increase. The on-board self-diagnosis system, upon detection of failures in the functioning of the system, enters the corresponding fault code into the module 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 you to read 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
In the electronic ignition system, a very high voltage is generated! Be careful, observe all necessary precautions when servicing any system components, including not only the main (ignition module, coil and BB wires), but also related, such as candle connectors, a tachometer and other equipment. Persons with an implanted pacemaker must not be allowed to service the components of the ignition system!
To avoid damage to ignition system components and to reduce the risk of injury, observe the following precautions.
- If the engine does not start, do not keep the ignition on for more than 10 seconds.
- Turn off the ignition before disconnecting the electrical wiring of any of the system components.
- Before connecting and disconnecting diagnostic equipment (e.g. stroboscope) turn off the ignition
- Do not ground the ignition coil windings to ground.
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