The control device in the system is the electronic control unit (ECU). Based on the information received from the sensors, the ECU calculates the parameters for regulating fuel injection and controlling the ignition timing. In addition, in accordance with the embedded algorithm, the ECU controls the operation of the electric motor of the engine cooling system fan, the electromagnetic clutch of the air conditioner compressor, performs the function of self-diagnosis of the system elements and notifies the driver of any malfunctions.
The engine management system, along with the electronic control unit, includes sensors, actuators, connectors and fuses.
Electronic control unit (ECU, controller) is connected by electrical wires to all the system sensors. Receiving information from them, the unit performs calculations in accordance with the parameters and control algorithm stored in the memory of the programmable read-only memory (ROM), and controls the executive devices of the system. The program version recorded in the ROM memory is designated by the number assigned to this modification of the ECU.
The control unit detects the fault, identifies and stores its code, even if the failure is unstable and disappears.
After repair, the fault code stored in the control unit memory must be erased.
The unit supplies various sensors and switches of the control system with direct current of 5 and 12 V. Since the electrical resistance of the supply circuits is high, the control lamp connected to the system terminals does not light. To determine the supply voltage at the ECU terminals, use a voltmeter with high impedance (10 MOhm). The control unit is located in the engine compartment behind the battery under a common cover with relays and fuses and is connected to the wiring harness by one 40-pin connector. The ECU is not suitable for repair; in case of failure, it must be replaced.
The coolant temperature sensor is installed in the engine cooling system. The sensor's sensitive element is a thermistor, its electrical resistance changes inversely proportional to the temperature.
The electronic unit supplies the sensor circuit with a constant "reference" voltage. The sensor signal voltage is maximum on a cold engine and decreases as it warms up. Based on the voltage value, the electronic unit determines the engine temperature and takes it into account when calculating the injection and ignition adjustment parameters.
The intake manifold air temperature sensor is similar in design to the coolant temperature sensor, and also uses a thermistor whose resistance changes depending on temperature.
The ECU supplies the sensor circuit with a constant "reference" voltage. The sensor signal voltage is maximum when the air in the intake pipe is cold, and decreases as its temperature increases. Based on the voltage value, the control unit determines the air temperature at the intake and makes adjustments when calculating the ignition advance angle.
The inductive type top dead center and crankshaft speed sensor is designed to synchronize the operation of the electronic control unit with the TDC of the piston of the 1st cylinder and the angular position of the crankshaft.
The sensor is installed at the rear of the engine opposite the timing ring on the engine flywheel. The ring is a toothed wheel with cavities. Two teeth are cut to create a synchronization pulse (a "reference" pulse), which is necessary to coordinate the operation of the control unit with the TDC of the pistons in the 1st and 4th cylinders.
When the crankshaft rotates, the teeth change the magnetic field of the sensor, inducing AC voltage pulses. The control unit determines the crankshaft rotation frequency based on the sensor signals and sends pulses to the injectors.
If the sensor fails, the engine cannot be started.
The throttle position sensor is mounted on the side of the throttle assembly and is connected to the throttle shaft.
The sensor is a potentiometer, to one end of which the "plus" of the supply voltage is supplied, the other end is connected to the "ground".
From the third output of the potentiometer (from the slider) the output signal goes to the electronic control unit.
When the throttle valve is turned (from the impact on the control pedal), the voltage at the sensor output changes. When the throttle valve is closed, it is minimal. When the valve opens, the voltage at the sensor output increases and reaches its maximum value when the valve is fully open.
By monitoring the sensor output voltage, the controller adjusts the fuel supply depending on the throttle valve opening angle (i.e. at the driver's discretion).
The throttle position sensor does not require adjustment, since the control unit senses idle speed (i.e. complete closing of the throttle valve) as a zero mark.
Absolute pressure sensor (rarefaction) in the intake pipe converts the pressure in this pipe into an electrical voltage, the value of which the electronic control unit determines the engine load. The sensor is installed on the intake pipe. When the engine is not running, the control unit determines the atmospheric pressure based on the sensor voltage and adapts the injection control parameters to a specific altitude above sea level. The atmospheric pressure values stored in the memory are periodically updated during uniform vehicle movement and during full throttle opening.
The vehicle speed sensor is installed on the gearbox. The sensor operates on the Hall effect. The sensor sends rectangular voltage pulses to the electronic control unit with a frequency proportional to the rotation speed of the drive wheels.
Oxygen concentration control sensor (lambda probe) is used in the closed-loop fuel injection system and is screwed into the threaded hole of the exhaust manifold. Information about the presence of oxygen in the exhaust gases is used to adjust the calculations of the injection pulse duration. Oxygen contained in the exhaust gases reacts with the sensitive element of the sensor, creating a potential difference at the sensor output. The potential difference varies from approximately 0.1 V (high oxygen content - lean mixture) up to 0.9 V (low oxygen - rich mixture).
Information from the sensor is sent to the electronic control unit in the form of low and high level signals. With a low level signal, the control unit receives information about a high oxygen content and, therefore, about a lean mixture. A high level signal indicates a low oxygen content in the exhaust gases and, therefore, about an over-rich mixture.
By constantly monitoring the sensor signal voltage, the control unit adjusts the amount of fuel injected by the injectors. When the sensor signal level is low, (lean air-fuel mixture) the amount of fuel supplied increases when the signal level is high (rich mixture) - decreases.
The lambda probe is the most vulnerable sensor in the vehicle's injection system. Its service life is from 20 to 80 thousand km, depending on the quality of gasoline and engine oil, operating conditions, driving style, engine health, etc. Poor condition of oil scraper rings, antifreeze getting into cylinders and exhaust pipes, enriched fuel-air mixture, and failures in the ignition system greatly reduce its service life. According to the manufacturer's recommendation, the oxygen concentration sensor should be changed every 75 thousand km, regardless of its condition.
Application. The use of leaded gasoline is strictly prohibited: lead "poisons" the sensor electrodes after several fill-ups with leaded gasoline. The catalytic converter of exhaust gases suffers from lead.
Due to the aging of the oxygen concentration sensor, its output electrical resistance decreases at a significantly higher temperature of the sensitive element to a value at which the sensor acquires the ability to reject the reference voltage. Due to the increased output electrical resistance, the output voltage swing of the sensor signal decreases. An aging sensor can be easily identified by the oscillogram of its output signal voltage in such engine operating modes when the flow and temperature of the exhaust gases decrease. These are idle and low load modes. As practice has shown, a faulty oxygen concentration sensor operates at high engine speeds, but as soon as the engine load decreases (idle mode), the signal amplitude quickly begins to decrease until the oscillations disappear.
The list of possible faults of the oxygen concentration sensor is quite large and some of them (loss of sensitivity, decreased performance) are not recorded by the car's self-diagnostics, so the final decision to replace the sensor can only be made after a thorough check, which is best left to specialists.
Application. There is no technology for repairing faulty lambda probes - if they break, they must be replaced.
If the oxygen concentration sensor is faulty, the ECU switches to a mode in which its voltage is not taken into account to determine the mixture parameters, i.e. to a control mode without feedback on the sensor output voltage. In this mode, the ECU continues to control the mixture composition taking into account the engine temperature, load, and parameters of other sensors.
The diagnostic oxygen concentration sensor operates on the same principle as the control sensor. The signal generated by the diagnostic oxygen concentration sensor indicates the presence of oxygen in the exhaust gases after the catalytic converter. The efficiency of the catalytic converter is assessed by the engine control unit by comparing the signals from the control and diagnostic sensors. If the catalytic converter is operating normally, the readings of the diagnostic sensor will differ significantly from the readings of the control sensor. The same readings indicate a malfunction of the catalytic converter.
The knock sensor, attached to the cylinder block between cylinders 2 and 3, detects abnormal vibrations (detonation strikes) in the engine.
The sensor's sensitive element is a piezoelectric crystal plate. When detonation occurs, voltage pulses are generated at the sensor's output, which increase with the intensity of detonation shocks. The ECU, based on the sensor's signal, adjusts the ignition timing to eliminate detonation flashes of fuel.
Application. Engine detonation is a self-accelerating process of transition of fuel-air mixture combustion into a detonation explosion without performing work, with the transition of fuel combustion energy into gas temperature and pressure. The flame front spreads at the speed of explosion, i.e. exceeds the speed of sound propagation in a given medium, and leads to strong impact loads on the parts of the cylinder-piston and crank-connecting rod groups, thereby causing increased wear of these parts. High gas temperature leads to burnout of the piston bottom and burning of the valves.
The diagnostic connector is located in the glove compartment on its rear wall. A scanning device can be connected to the diagnostic connector, which reads information and serves to output fault codes from the ECU memory, detected during operation of the engine management system.