The fuel pump, mounted in the fuel tank, pumps fuel from the fuel tank to the throttle body through a filter mounted on the rear wall of the engine compartment. The fuel pump pressure is controlled by a pressure regulator mounted on the side of the throttle body. The pressure regulator rises to allow excess fuel to return to the fuel tank when the pressure in the fuel system exceeds the optimum. To reduce emissions and improve cold engine drivability, an electronic heater element is installed between the throttle body and the intake manifold to quickly warm up the throttle body during cold engine 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 valve and the speed of closing/opening of the throttle valve;
- 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;
- crankshaft angle sensor (installed in the ignition distributor) - informs the control unit about the engine speed and the position of the crankshaft;
- vehicle speed sensor (installed in the speedometer) - informs the control unit about the vehicle's speed;
- the power steering switch and the air conditioning switch - inform the control unit that these systems are on 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 about the oxygen content in the exhaust gases to the control unit.
The signals from all these sensors are analyzed by the ECU. Based on this information, the ECU adjusts the operation of the fuel injector (by changing the pulse duration - the period of time during which the injector is open - in order to obtain a richer or leaner fuel mixture, depending on what is needed). The composition of the fuel mixture and the idle speed of the engine are constantly changed by the ECU in order to ensure optimal engine starting (during cold or hot start), engine warm-up, engine idling, best engine performance when driving on the highway and when accelerating rapidly.
The electronic engine control unit also fully controls the engine's idle speed through an optional air supply valve. This valve, which is mounted on the throttle body, controls the opening of the air channel that passes by the throttle. When the throttle valve is closed, the electronic control unit controls the opening of the valve, which regulates the amount of air passing through the throttle body channel, and thus controls the engine's idle speed.
The throttle body has a device that can independently increase the engine idle speed when the engine is warming up. This function is controlled by a temperature valve. When the engine is cold, the wax capsule in the valve is small (the valve is installed in the throttle body), and the fast idle cam holds the throttle valve slightly open. As the engine warms up, the wax capsule expands, lifting the valve plunger upward, which in turn rotates the fast idle cam to the desired position. In addition, an idle speed increase solenoid valve is mounted on the throttle body, which is controlled by the electronic control unit. The solenoid valve controls the opening of the air passage that passes the throttle valve and is used to increase engine speed when the power steering or air conditioning systems 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 emission control system,
If the signals received by the electronic control unit from the sensors are outside the permissible limits 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 the incorrect sensor signals and accepts a certain set value as the sensor signal, which will allow the engine to operate, although with less efficiency. If the electronic control unit switches to a protected mode of operation, a warning light comes on on the instrument panel and the corresponding fault code is entered into the memory of the electronic control unit.
If the warning light comes on, you should contact a specialist as soon as possible. A repair shop can perform a full diagnosis of the engine management system using electronic diagnostic equipment, which simply needs to be connected to the diagnostic connector.
Attention! The electronic engine control unit also has a self-diagnosis mode that can be used by the car enthusiast (see subsection 6.3.1.12).