Table of contents: General information ↓ Precautionary measures ↓
General information
The fuel system consists of a fuel tank mounted at the rear of the vehicle, a fuel filter with a built-in water separator mounted under the hood, a high-pressure fuel pump (HPFP), fuel lines, injectors and associated components. All engines are turbocharged.
The injection pump is driven by a belt from the crankshaft and rotates at half the crankshaft speed. Fuel is drawn from the fuel tank through the fuel filter via the injection pump, which then delivers fuel under very high pressure through pipes to the injectors. Direct fuel injection via various actuators is controlled by commands from the electronic control unit (ECU). The unit receives data from sensors via wires.
The basic setting of the injection timing is made mechanically by installing the pump on the mounting bracket. Dynamically, the injection advance and duration are controlled by the ECU and depend on the engine speed, throttle position, intake air flow, intake air temperature, coolant temperature, fuel temperature, atmospheric pressure and vacuum in the intake manifold - all this information received from various sensors is processed by the ECU. The closed injection control loop is determined by the injector needle lift sensor. Injector No.3 is equipped with a needle lift sensor.
Two-stage injection nozzles are used to improve (soften) the combustion process and improve the composition of exhaust gases.
Additionally, the ECU monitors the operation of the exhaust gas recirculation (EGR) system, the boost pressure control system, and the glow plug glow control system.
It should be noted that troubleshooting the engine management system is only possible with specialized diagnostic equipment. If a fault occurs, contact your dealer for assistance. If a fault is detected, replacing the faulty unit is described in detail in the following paragraphs,
Note: In this chapter, engines are often referred to by their code.
Precautionary measures
Most of the operations described in this chapter require opening the fuel system, which may cause some fuel spillage. Before starting work, read the warnings below and the information in the "Safety first!" at the beginning of this Guide.
When working with the fuel system, avoid contact of diesel fuel with skin surfaces - always wear protective clothing and gloves. The workplace must be well ventilated so that fuel vapors do not accumulate.
Fuel injectors operate at very high pressures - the fuel jet from the injector can penetrate the skin, leading to fetal results. Do not place your hands under the working injectors - entrust the work of checking and adjusting the fuel equipment to a specialist.
Under no circumstances should diesel fuel come into contact with the cooling system hoses - wipe up any accidental leaks immediately. If a hose has been in contact with fuel for a long time, it must be replaced. The diesel fuel system is particularly sensitive to dirt, air and water. When working with the fuel system, pay special attention to cleanliness. Before disconnecting the fuel system components, wipe the area around it clean. Store the removed components in a tightly closed container so that even condensation from the atmosphere does not accumulate in it. Use a lint-free cloth for wiping.
(Information obtained from this resource AudiManual)