General information
Engines without turbocharging
The main parts of the fuel system are the fuel tank, high-pressure fuel pump, fuel pre-filter and main fuel filter located in the engine compartment, supply and return fuel lines, as well as injectors, one for each cylinder.
The high-pressure fuel pump (HPFP) is chain-driven from the camshaft and rotates at half the camshaft speed. Fuel from the fuel tank passes through the fuel pre-filter and main fuel filter into the high-pressure fuel pump, which directs it under very high pressure through separate feed pipes to the injectors.
The basic fuel injection timing is adjusted by turning the high-pressure fuel pump on its supporting bracket. During engine operation, the fuel injection timing is adjusted by the high-pressure fuel pump itself and is primarily determined by the accelerator position and engine speed. Injection timing can be changed using a threaded regulator located on the side of the high-pressure fuel pump.
The injectors are mechanical spring valves that open when the pressure of the incoming fuel exceeds a certain level. At the same time, fuel from the injector nozzle is injected through the pre-chamber into the cylinder (indirect injection).
The engine is stopped by a vacuum-controlled shut-off valve located on the lower wall of the fuel injection pump. When the starter key is set to the "OFF" position, the vacuum switch integrated with the starter key closes the vacuum line to the shut-off unit, which in turn stops the fuel supply to the high-pressure fuel pump, which causes the engine to stop.
The engine operation in idle mode is controlled primarily by a mechanical regulator combined with the high-pressure fuel pump. The regulator's operating principle is based on the use of centrifugal force generated by the rotation of weights fixed to the pump axis, which change the position of the high-pressure fuel pump control rod via a spring-loaded lever. The regulator mechanism can be affected by one or more drive devices, which makes it possible to gradually increase the engine speed in idle mode taking into account the load, i.e. when the power steering or air conditioning are operating, or when the automatic transmission drive is engaged, as well as when starting a cold engine, when mechanical friction is high.
Models with air conditioning and automatic transmission are equipped with an electronic idle speed control system (ELR). Using a sensor located on the flywheel and a sensor mounted in the cylinder head, this system monitors the engine speed and coolant temperature. A microprocessor compares the engine speed with the optimum value stored in its memory. If these values differ, the microprocessor generates a control signal for the electromagnetic actuator, which mechanically acts on the regulator to change the idle speed accordingly.
An electronic anti-jerking system (ARA) is usually installed on models with a manual transmission. This system uses information about the engine speed and coolant temperature to minimize the tendency of the car to jerk when accelerating a partially loaded car and decelerating. To do this, an electromagnetic actuator attached to the high-pressure fuel pump partially reduces the amount of fuel supplied to the engine, resulting in a decrease in the developed torque and a decrease in the ability to jerk. Control of engine overload is carried out by an integrated electronic unit.
Turbocharged engines
The fuel system operates in the same way as on non-turbocharged engines. However, the idle speed control system and the anti-jet system are now controlled by the Electronic Diesel System (EDS), which also monitors the intake pressure (turbo pressure) and an exhaust gas recirculation system.
Precautionary measures
Many of the operations described in this chapter involve disconnecting the fuel lines, which may result in some fuel leaking. Before starting work, read the Warnings below and the "Safety First!" information at the beginning of this manual.
Warning: Diesel fuel should never come into contact with coolant hoses - wipe off any splashes immediately. Hoses that have been contaminated with fuel for an extended period of time should be replaced. Diesel fuel systems are particularly sensitive to dirt, air and water. When working on any part of the fuel system, pay particular attention to cleanliness. Thoroughly wipe the area around fuel system connections before disconnecting them. Store dismantled parts in tightly sealed containers to prevent dirt from entering the system and condensation from forming. Use only a lint-free cloth and clean fuel for flushing. Do not use compressed air to clean the system during work.
Caution: When working on any part of the fuel system, avoid skin contact with diesel fuel - wear protective clothing and gloves when handling fuel system components. Ensure good ventilation in the work area to avoid high concentrations of diesel fuel vapors.
Warning: The injectors operate under extremely high pressure and the jet of fuel from the injector nozzle can injure the skin with all possible unpleasant consequences. Exercise extreme caution when working with injectors. Never place your hand or any other part of the body under the injector nozzles. You must strictly adhere to the rule that work involving pressure testing of injectors must be carried out by dealers or specialists in diesel fuel equipment.