The pressure reducing valve maintains the pressure in the fuel system constant within the range of approximately 3.8-3.9 bar.
Fuel is supplied through electronically controlled valve injectors, i.e. intermittently injected into the distribution line directly in front of the engine intake valves.
The engine control unit controls the operation of the injectors, ensuring sequential fuel injection. This means that the valve injectors operate in turn in accordance with the ignition order. At the same time, the amount of fuel injected is regulated.
Air is sucked in by the engine through the air filter and through the throttle valve fitting and the intake manifold to the intake valves. The amount of incoming air is regulated by the throttle valve, the opening angle of which is performed by a stepper motor on the "command" of the control unit.
The volume of incoming air is measured by the air mass flow meter, which is built into the engine control unit. In the air mass flow meter housing, a thin sensitive film is located as a heating element, cooled by the passing mass of the sucked air.
To ensure that the film temperature remains constant despite air cooling, the engine control unit regulates the heating current in accordance with the amount (mass) of incoming air.
If, for example, due to an increase in the volume of incoming air, the film begins to cool down, the supplied voltage is immediately increased to maintain the film heating temperature. Based on the change in the film heating current, the control unit determines the engine load and adjusts the injected fuel volume accordingly.
[Publication taken from an online resource: MercedesMAN.ru]
The electronic engine control unit is a small, fast computer. It determines the optimum ignition timing, fuel injection, and the amount of fuel injected.
The information received by the electronic unit from the sensors, as well as the commands sent to the actuators or control mechanisms, ensure optimal engine operation in any situation that arises while driving.
If one or more main sensors fail, the control unit executes an emergency program to reduce the risk to the engine and ensure continued movement.
In such cases, the engine starts to run intermittently and may stall when you press the accelerator pedal.
Fuel injection system sensors and actuators
The crankshaft position sensor is installed in the cylinder block next to the flywheel. This sensor transmits information to the control unit about the number of revolutions at which the crankshaft rotates, and also informs about the position of the piston of cylinder No.1 at TDC.
The camshaft position sensor is located on the end face of the cylinder head cover. Together with the crankshaft position sensor, it transmits information to the control unit about the position of the piston of cylinder No.1 at TDC, which serves as the basis for synchronizing the ignition timing and fuel injection sequence.
The throttle actuator consists of an electric motor with two potentiometers. The electric motor regulates the position of the throttle valve. This ensures that the idle speed remains constant regardless of the number of consumers connected to the on-board network, such as, for example, the power steering or the air conditioning compressor.
The throttle angle sensor/potentiometer is located directly on the actuator and transmits information about the throttle opening angle at the current moment to the control unit. The second potentiometer is a spare and duplicates the information. In case of failure of the first potentiometer, it performs its function.
The accelerator pedal position sensor is located in the driver's footwell. The sensor detects the position of the accelerator pedal via a short pulley and transmits the information to the engine control unit as a signal with a variable voltage. For safety reasons, the sensor duplicates the signal it transmits.
The coolant temperature sensor, located in the thermostat housing, is a resistance with a negative temperature coefficient. This means that the resistance of the sensor decreases as the coolant temperature increases. The intake air temperature sensor is also a resistance (resistor) with a negative temperature coefficient and is part of the engine control unit.
The fuel tank is ventilated using a container with activated carbon and an electromagnetic valve, also called a regeneration valve. The activated carbon absorbs fuel vapors that form in the tank as a result of heating the fuel. When the engine is running, the fuel absorbed by the carbon is released and enters the engine for combustion.
Lambda probe (oxygen sensor) is designed to control the operation of the catalyst, determining the oxygen content in the OT and transmitting the corresponding information to the control unit.
The knock sensor is located on the cylinder block near the oil level indicator guide and serves to prevent knock combustion of fuel by maintaining the optimum ignition advance angle. This makes better use of the energy generated by the combustion of fuel and reduces fuel consumption.
As part of vehicle maintenance, there is no need to adjust idle speed, ignition timing, or CO content in exhaust gases. These indicators are maintained unchanged by electronics.
If the performance indicators begin to differ significantly from the nominal ones, then the reason for this is a defect in the parts that need to be replaced. Checking the fuel injection system is only possible using the appropriate diagnostic equipment.
Visual inspection of the fuel injection system
Troubleshooting the fuel injection system or eliminating possible faults requires the use of special control and measuring devices. Such devices are very expensive and, as a rule, are available only in specialized workshops.
The car owner can only perform visual inspection and testing of the injection system elements on his own.
1. Check the battery, see the relevant chapter.
2. Check all fuses, see the relevant chapter.
3. Disconnect and then reinstall all plugs or connectors of the relevant system. Make sure that the fit and fastening of the plug connections and wires in the engine compartment are in order.
4. Inspect all ground (-) points and make sure that the wires are not loose or the contacts are not corroded.
5. Inspect all hoses and pipes and make sure that they are tightly connected, have no cracks or breaks, and that the rubber of the hoses has not become porous. Tighten any loose hose and pipe fastenings.