The fuel pump, located in the fuel tank, pumps fuel from the fuel tank into the throttle body through a filter mounted on the rear wall of the engine compartment. Fuel pump pressure is controlled by a pressure regulator that is mounted on the side of the throttle body. The pressure regulator rises so that excess fuel can return to the fuel tank when the pressure in the fuel system exceeds the optimum. To reduce emissions and improve cold engine handling, an electronic heating element is installed between the throttle body and intake manifold to quickly warm up the throttle body during cold starts.
The electronic engine management system consists of an electronic control unit and the following sensors:
- throttle potentiometer - informs the electronic control unit about the position of the throttle and the speed of closing / opening the throttle;
- coolant temperature sensor - informs the control unit about the engine temperature;
- air flow sensor - informs the control unit about the amount and temperature of air entering the throttle body;
- crank angle sensor (installed in the ignition distributor) - informs the control unit about the speed of the engine and the position of the crankshaft;
- vehicle speed sensor (installed in the speedometer) - informs the control unit about the vehicle speed;
- a switch in the power steering system and a switch in the air conditioning system - inform the control unit about the inclusion of these systems so that the control unit can adjust the engine idle speed to compensate for the additional load on the engine from these systems;
- exhaust gas sensor (only on models with catalytic converter) - sends information to the control unit about the oxygen content in the exhaust gases.
The signals from all these sensors are analyzed by the electronic control unit. Based on this information, the electronic control unit regulates the operation of the fuel injector (by changing the pulse width - the period of time during which the injector is open - in order to get a richer or leaner fuel mixture, depending on what is needed). The composition of the fuel mixture and the engine idle speed are constantly changed by the electronic control unit in order to provide optimal engine starting (cold or hot start), warming up the engine, idling the engine, the best engine performance when driving on the highway and during a sharp increase in speed.
The ECM also fully controls the idle speed of the engine through an additional air supply valve. This valve, which is mounted on the throttle body, controls the opening of the air passage that runs past the throttle body. When the throttle is closed, the ECM controls the opening of a valve that regulates the amount of air passing through the throttle body passage and thus controls the idle speed of the engine.
The throttle body has a device that can independently increase the engine idle speed when the engine warms up. This function is controlled by a temperature valve. When the engine is cold, the wax capsule in the valve is small (valve installed in the throttle body), and the fast idle cam keeps the throttle slightly ajar. As the engine warms up, the wax capsule expands, pushing the valve plunger up, which in turn turns the fast idle cam into position. In addition, a solenoid valve for increasing the engine idle speed is installed on the throttle body, which is controlled by an electronic control unit. The solenoid valve controls the opening of an air duct that passes the throttle and is used to increase engine speed when power steering systems or air conditioning are on.
On models with a catalytic converter, which are described in subsection 6.4.1 and subsection 6.4.2, the electronic control unit also controls the exhaust system and the fuel vapor control system,
If the signals received by the electronic control unit from the sensors are out of range or do not agree with each other, the electronic control unit switches to a protected mode of operation. In this case, the electronic control unit ignores incorrect sensor signals and takes a certain setpoint as the sensor signal, which will allow the engine to work, albeit with less efficiency. If the electronic control unit enters the protected mode of operation, a warning light on the instrument panel lights up and the corresponding fault code is stored in the memory of the electronic control unit.
If the warning light comes on, contact a specialist as soon as possible. In the repair shop, a complete diagnosis of the engine management system can be carried out using electronic diagnostic equipment, which simply needs to be connected to the diagnostic socket.
Attention! The engine's electronic control unit also has a self-diagnostic mode that can be used by a car enthusiast (see subsection 6.3.1.12).