The fuel tank on the Sedan and Coupe models is mounted vertically behind the rear seat back. On the Estate models, the fuel tank is mounted horizontally under the boot floor. The fuel level sensor is mounted on top of the fuel tank and can be replaced without removing the fuel tank.
The electric roller fuel pump is installed under the bottom at the rear of the vehicle. The fuel pump is cooled by the fuel flowing through it. The fuel pump has a one-way valve that maintains pressure in the fuel system even after the engine is turned off. The pump also has a bypass valve that limits the maximum pressure in the fuel system.
A pressure accumulator is installed between the fuel pump and the fuel supply hose, which maintains pressure in the fuel system after the engine is turned off. After the pressure accumulator reduces the fluctuations in fuel pressure that occur in the fuel system when the fuel injectors operate.
The cartridge type fuel filter is installed near the pressure accumulator behind the fuel pump.
The fuel quantity is measured by the distributor, which mechanically regulates the amount of fuel supplied to the fuel injectors based on the deviation of the air flow measurement sensor. The mixture composition is regulated dynamically by the actuator of the electrohydraulic shock absorber pressure with constant control of the electronic control unit (ECU). The ECU unit is controlled based on signals from sensors located on and near the engine. Constant dynamic adjustment of the fuel mixture improves engine operation, reduces fuel consumption and the amount of harmful substances in the exhaust gases. In addition, the differential pressure valve in the distributor element ensures a constant fuel supply in all operating modes.
Starting a cold engine is facilitated by a cold start valve and an auxiliary air device. The cold start valve is an electrically controlled fuel injector installed in the intake manifold and sprays additional fuel into the air entering the engine. Fuel start mode switch (temperature and time sensor) controls the amount of time the cold start valve remains open. The air assist device is a valve that allows air to bypass the throttle valve, causing the idle speed to increase. The bimetallic strip and heater coil control the amount and time the valve opens. The air assist device only operates when starting a cold engine.
On later models, a rotary actuator is installed. This unit replaces the auxiliary air unit and is controlled by the ECU unit, as a result of which the idle speed is stabilized in all operating modes, including accelerated idle mode during warm-up and idle speed control under load.
Models with a catalytic converter have feedback, which, based on the signal from the oxygen sensor, regulates the fuel mixture ratio.
Precautions
The fuel system is under constant pressure, even after the engine is turned off, so before carrying out any work on the fuel system, it is necessary to relieve the pressure.
To prevent the possibility of accidental short circuits in the electrical circuit and damage to the electronic components of the fuel injection system, always remove the ground cable from the battery.
Warning! Gasoline is extremely flammable and explosive, so care must be taken when working on any part of the fuel system.
Attention! Work on the fuel system must be carried out in a well-ventilated area, for which you can open all the windows and doors to create a draft.
Warning! When working on the fuel system, do not use open flames, electric welding or tools that may generate sparks. Make sure that a charged fire extinguisher is in the immediate vicinity of the work area.
Warning! Use goggles to protect your eyes from fuel getting into them. If fuel gets on your skin, rinse the area with plenty of water.
Warning: The container that held the fuel contains fuel vapor and is potentially explosive.
Caution! When working with the fuel system, keep it clean, as dirt that gets into the fuel system channels can block them, which will disrupt the normal operation of the engine.
(Material taken from a web resource mercedesman.ru)