Engines without turbocharging
The diesel engine fuel system includes a fuel tank, a high-pressure fuel pump, a fuel filter mounted on the fuel pump and a main fuel filter, supply and return fuel lines and fuel injectors, one installed on each cylinder.
The fuel pump is chain driven and rotates at half the engine crankshaft speed. Fuel from the fuel tank is drawn by the fuel pump through the primary and main filters and then delivered to the fuel injectors under high pressure.
The fuel injection moment is set by turning the fuel pump on the mounting brackets. When the engine is running, the injection moment is determined mechanically by the fuel pump depending on the accelerator pedal position and engine speed. The fuel injection moment can be changed using the adjusting device located on the side of the fuel pump.
The fuel injector is a valve that opens at a strictly defined fuel pressure. The atomizer, located at the lower end of the injector, forms a torch of sprayed fuel of the required shape. The fuel is cut off by a needle under the action of the injector spring. The atomizer and needle are precision units and require careful handling during repair. Excess fuel after the cutoff is pumped along the needle, lubricating it and is discharged into the fuel tank through the return pipeline.
The serviceability and correct adjustment of the injectors are very important for the normal operation of the engine. If the injector sprayer does not provide the required torch shape or there is a bad cut-off, the engine starts to vibrate, strong mechanical knocks appear, and the pressure increases. It should be noted that the sprayers from different engine models are externally identical, but have different characteristics, in particular, the shape of the torch, so new sprayers should be used only those designed for a given model.
The engine is shut off using a vacuum switch, which is installed on the top of the high-pressure fuel pump. When the ignition key is turned to the "OFF" position, the vacuum switch, connected to the ignition switch, closes the vacuum supply to the vacuum switch, which in turn closes the fuel supply to the fuel pump, and the engine stops.
The engine idle speed is adjusted by a mechanical regulator, which is built into the high-pressure fuel pump. The mechanical centrifugal regulator changes the position of the fuel pump rack via a spring-loaded lever. Idle speed is adjusted by one or more actuators, which change the idle speed when a load is applied. For example, when the power steering, air conditioning, the drive on models with an automatic transmission, or when starting a cold engine, are turned on.
On later models with 6-cylinder engines and models with 4- and 5-cylinder engines with air conditioning and automatic transmission, an electronic idle speed control (ELR) system is installed. In this system, an electronic control unit monitors the engine speed with a sensor mounted near the flywheel and the coolant temperature with a sensor screwed into the cylinder head. The ECU compares the actual values with the values stored in memory and, if necessary, activates an electromagnetic actuator that moves the fuel pump regulator and changes the engine idle speed.
Some models with a manual transmission are equipped with an engine anti-jerk control (ARA). This system uses engine speed and coolant temperature information to eliminate the possibility of the car jerking during acceleration and deceleration. When approaching the jerk condition, an actuator mounted on the side of the fuel pump briefly reduces the amount of fuel supplied. As a result, the engine torque decreases and the tendency to jerk disappears. On models with 6-cylinder engines, the engine is controlled by an electronic ELR device, and on other models by a specialized electronic device.
Turbocharged engines
The fuel injection system on turbocharged engines operates in a similar manner to the fuel injection system on naturally aspirated engines. On turbocharged engines, idle speed control and engine anti-jerk control are controlled by the Electronic Diesel System (EDS), which also controls the exhaust gas recirculation system pressure and the turbocharger.
When working on the fuel system, fuel may leak, so care must be taken.
Caution! Do not allow diesel fuel to come into contact with the cooling system hoses. Hoses that have been exposed to diesel fuel for a long time must be replaced.
Attention! The diesel engine fuel system is particularly sensitive to contamination, so when working on the fuel system, maintain maximum cleanliness. Before disconnecting the fuel lines, thoroughly clean them from dirt.
Caution: Do not use compressed air to clean fuel system components installed on the engine.
Warning! When checking the operation of fuel injectors, never place your hands or any part of your body under the jet of fuel coming out of the injector. Fuel comes out of the injector under high pressure and can penetrate the body through the skin.
Article based on data from the website [MercedesMan.ru]