General information and safety precautions: power supply system (Audi Q7-4L-D)

The fuel system includes: a fuel tank with fuel delivery modules installed at the rear of the vehicle, fuel lines, a fuel cooler, a fuel filter, as well as an electronic distributed sequential fuel injection system controlled by the Engine Control Module (ECM). The distributed sequential fuel injection system on TDI-CR models includes: a high-pressure fuel pump (HPFP) with an integrated lift pump, fuel distribution rails "Common Rail", piezo injectors. pressure fuel pipes and return fuel lines.

The location of the power supply system components is shown in Figures 1.1a-u.

























































The diagram of the fuel supply system is shown in figures 1.2ad.









The components of the fuel injection system are shown in Figures 1.3a-e.











The components of the vacuum section of the fuel system of the 3.0 l 2nd generation engines are shown in Figure 1.4.



The fuel tank contains one or two fuel delivery modules, each of which is an assembly of two fuel level sensors and a fuel pump with a mesh filter. Fuel gauges are designed to display the fuel level on the instrument cluster. The electric fuel pump is designed to create pressure in the low-pressure part of the fuel supply system. The mesh fuel filter is designed to last the entire life of the vehicle and does not require replacement.

Jet pumps are designed to keep the trays in which the fuel supply modules are placed constantly filled with fuel, so that under no circumstances does air enter the fuel system.

The fuel booster pump is designed to supply fuel from the low-pressure circuit to the high-pressure fuel pump under a pressure of at least 5 bar, which is necessary for the operation of the high-pressure fuel pump in any mode.

The high-pressure fuel pump increases the fuel pressure to a maximum of 1600 bar or 2000 bar and delivers it through one pipe to the fuel distribution line of one cylinder bank, which is connected to the line of the other cylinder bank. In the distribution lines, the fuel pressure is equalized for all injectors and is monitored by a fuel pressure sensor.

Pressure fuel lines (metal tubes) manufactured with pre-set lengths and bending radii in the required locations; such fuel lines should be installed in such a way that they are not subject to any stress.

The injectors inject fuel under high pressure directly into the combustion chambers. The moment and duration of fuel injection are determined by the ECM unit based on signals from various sensors (see Section 2).

Excess fuel from the injectors is returned to the fuel tank through the injector return lines, the pressure holding valve and the fuel pump. The fuel pressure holding valve is designed to maintain the pressure in the return lines of the injectors, which is necessary for the operation of the injectors. Do not disconnect the fuel pressure holding valve while the engine is running to prevent damage to the injectors. The return fuel lines of the injectors are replaced only together with the pressure holding valve. If the fuel retention valve and fuel return lines from the injectors have been replaced, after starting the engine, allow it to idle for approximately two minutes to purge air from the fuel system.

Rail-mounted fuel injection system "Common Rail", compared to the injection system with a distributor fuel injection pump, it has the following distinctive features:

• The injection pressure can be freely selected and adapted to the corresponding engine operating mode;
• High injection pressure (up to 1600 or 2000 bar) creates conditions for good mixture formation;
• Flexible batch injection process with multiple pre- and post-injections;
• Low fuel consumption;
• Low level of harmful emissions;
• Smooth running engine.

Injection system "Common Rail" it involves a variety of injection control algorithms in order to adapt the pressure and injection process to the engine operating mode. At the same time, such a system fully complies with the ever-increasing demands for reduced fuel consumption, reduced levels of harmful emissions and increased engine smoothness.

Fuel saving tips

Driving style has a significant impact on fuel consumption. Below are some tips to help you save fuel.

• After starting the engine, move off immediately, even if it is in cold weather (do not allow a cold engine to run at high speeds and do not drive at high speeds until the engine has warmed up).
• If you stop the vehicle for more than 40 seconds, turn off the engine.
• Always drive in the highest gear possible for the given speed.
• When driving long distances, maintain a steady speed whenever possible. Avoid driving at high speeds, do not brake unnecessarily.
• Do not carry unnecessary loads in your vehicle.
• Check the air pressure in your tires and do not allow the pressure to drop excessively.

Air supply

The air supply system includes the air intake, air cleaner, throttle body, intake manifold, turbocharger and intercooler, as well as (see Part B) eGR and PCV systems.

Each throttle valve is controlled by the ECM via an electric motor based on a signal from the accelerator pedal position sensor. The throttle position is controlled by the TPS sensor. On diesel models, the throttle body has the following functions.

• In some modes, the throttle valve is used to create a pressure differential between the intake tract and the EGR circuit. This pressure differential promotes more efficient operation of the EGR system.
• In DPF regeneration mode, the throttle valve regulates the inlet air flow.
• When the engine is turned off, the damper closes, gradually reducing the amount of incoming air to smoothly stop the engine.

All diesel engines use turbocharging, with charge air cooling by an intercooler. The turbocharger consists of two elements (turbines and compressors), mounted on one shaft and enclosed in a common housing. The turbocharger bearings receive oil for cooling and lubrication from the engine through the supply oil line. The oil returns to the crankcase through the return oil line.

The turbocharger increases the pressure of purified atmospheric air, thereby increasing the amount of air entering the cylinder in one cycle. With more oxygen, more fuel can be burned. Thus, with the same working volume and rotation speed characteristics, better power figures are achieved. The air heated in the turbocharger is cooled as it passes through the intercooler. When cooling, the air density increases and, since more oxygen enters the combustion chambers, an additional increase in power occurs.

Ensuring safety and maintaining cleanliness when working with the fuel supply system

Caution: Fuel injection equipment is manufactured to very precise tolerances and with very small clearances, so absolute cleanliness is especially important when working with these components. Be sure to insert plugs into any open holes or lines.

Caution: When loosening and tightening the union nuts securing the fuel pressure lines, simultaneously press the flared end of the fuel line against the injector and remove (suck) vacuum removal to prevent dirt from entering the fuel system. Avoid allowing the union nuts to strike the flared edges of the new fuel lines, as this may damage the lines and introduce foreign particles into the lines. Close the holes formed after disconnecting the tubes with clean plugs.

• Do not work on the fuel system near an open flame, do not smoke, and do not use heating devices while working on the fuel system! Keep a fire extinguisher handy.
• Before working on the fuel system, always disconnect the negative battery cable to avoid sparks. Before disconnecting the battery, you should read the fault codes (see Chapter 5).
• Ensure proper ventilation of the workplace - fuel vapors are toxic.
• The fuel system is under pressure and fuel may escape if opened, so wear safety glasses. Wipe up any spilled fuel with a rag.
• Hose connections are secured using strap or clamp clamps. When disassembling, the clamping clamps should be replaced with band clamps.
• Clean connections and adjacent areas thoroughly before opening.
• Place the removed components on a clean surface and cover with plastic, paper or a lint-free cloth.
• Close open nipple connectors, for example, with suitable clean plugs.
• Install only clean parts - remove replacement components from packaging immediately before installation. Do not use parts that have been stored without packaging.
• Avoid using compressed air when the fuel system is open and try not to move the vehicle if possible.
• Do not use sealants containing silicone, as silicone particles that get into the engine do not burn off and may cause the lambda probes to fail.
• Before removing the fuel tank, pump out the fuel from it using a pump specially designed for this purpose.
• Remember that even an empty fuel tank remains explosive.
• After installing the fuel system components, start the engine and check all connections for leaks.