Additionally, a fuel accumulator is built into the fuel supply line together with the fuel pump. Its main function is to maintain pressure in the line for some time after the engine has stopped. This prevents the formation of vapor locks and improves hot engine starting. In addition, the fuel accumulator acts as a pressure damper, reducing fluid pressure pulsations in the fuel line as a result of the opening and closing of the injectors. A non-separable gasoline filter is installed close to the accumulator, below the fuel pump. It prevents dirt and insoluble sediments from entering the fuel system.
The fuel distributor unit functions as a fuel meter. It mechanically regulates the amount of fuel reaching the injectors. Its operation is based on the deflection of the air flow meter sensor. The main fuel - air mixture under the control of the electronic control unit (ECU) is dynamically regulated by an electromechanical pressure regulator. With its help, the quality of the mixture can be precisely regulated based on the signals from the sensors on and off the engine. The result of the system operation is better combustion of the mixture and increased engine efficiency, as well as reduced harmful emissions into the atmosphere. Since the accuracy of the fuel meter is highly dependent on the fuel supply pressure, the fuel system is equipped with a preliminary fuel pressure regulator, which controls the fuel supply to the distributor unit. In addition, differential pressure valves in the distributor unit ensure that the fuel supply to the measuring slots remains constant under all operating conditions. Efficient engine starting at low ambient temperatures is ensured by a cold engine start valve and an additional air valve. The cold start valve is an electric injector mounted on the intake manifold that injects additional fuel into the incoming air stream and enriches the mixture. A thermal switch with a time delay regulates the opening time of the cold start valve. The additional air valve allows air to be supplied behind the throttle valve, thereby increasing the idle speed. The built-in bimetallic plate and heater coil determine both the opening value and the opening time of the valve. The additional air valve operates only when starting a cold engine and during warming up.
Later versions are equipped with an idle speed control valve. This unit replaces the additional air valve and is controlled electronically by the ECU. It ensures constant idle speed under all operating conditions, including increased idle speed during warm-up and idle speed under load, such as when the power steering or air conditioning system is operating.
Models equipped with a catalytic converter have a closed-loop power supply system. This is achieved by processing the signal from the oxygen sensor (Lambda probe), built into the exhaust system, and maintaining the optimal fuel-air mixture ratio.
Precautionary measures
Many of the operations described in this Chapter involve disconnecting fuel lines, which may cause some gasoline to leak. Before starting work, carefully read and follow the precautions in the "Safety First" section.
Residual pressure in the fuel lines remains long after the vehicle has been used. Therefore, special care should be taken before disconnecting any part of the fuel system.
Loosen the fuel line connections slowly to avoid sudden opening which could cause petrol spillage – refer to paragraph 2 for details on how to perform the operation.
For personal and equipment safety, many of the procedures described in this Chapter involve disconnecting the negative battery terminal. First, this reduces the risk of electric shock when working on vehicle components and, second, it prevents damage to electronic components (such as sensors, actuators, ECUs, which are particularly sensitive to power failure when they are in operation.
Warning: Gasoline is a very dangerous and volatile liquid, so no precautions are too much when working with it. Ventilate the room well when working with gasoline - open windows and doors to create a draft. Do not smoke and do not allow open flames or uncovered lamps near the work area. Remember that household appliances such as heaters, kettles, hair dryers also pose a potential gasoline fire hazard. Always have fire extinguishers on hand and familiarize yourself with the rules for their use before starting work. Protect your eyes when working with the fuel system and immediately wash off gasoline that comes into contact with your skin with soap and plenty of water. Remember that gasoline vapors are just as dangerous as liquid gasoline; the canister from which gasoline is drained contains gasoline vapors and is potentially dangerous.
Caution: When working with fuel system components, pay special attention to cleanliness - dirt entering the fuel system can block the pipes, which will lead to interruptions in engine operation.