Audi A4, S4

since 2000 release

Repair and operation of the car

Power supply systems of petrol and diesel engines

General information and security measures

Petrol engines

Are a part of fuel system: fuel tank, fuel pump and fuel pipelines, and also fuel and air filters. Indications of rather fuel filter of the diesel engine are provided in the Head the Current leaving and service.

The fuel tank has volume about 70 l and is located before a back suspension bracket of the car. The current volume of fuel in a tank is displayed to the driver on a control panel. The fuel tank has system of ventilation. Gather on the petrol engine of couple of gasoline in an adsorber and move in engine combustion chambers.

The cable of an accelerator is absent. Instead of it on a pedal the sensor of its situation is installed.

Style of driving of the car has essential impact on fuel consumption. Some councils for the reasonable address with a gas pedal are given below.

• After start of the engine at once start even if it occurs on a frost.
• At a car stop for a while more than on 40 with, switch off the engine.
• Move always on the highest transfer.
• At the movement on long distances whenever possible support uniform speed. Avoid the movement at high speeds. Operate the car circumspectly. Without need do not brake.
• Do not transport excessive freight on the car. If the luggage carrier is not used, remove it from a roof.
• Check air pressure in tires. Do not allow excessive pressure decrease.

Diesel engines

During the operation of the diesel engine in its cylinders clean air which contracts to a high pressure is soaked up. Thus air in the cylinder heats up to temperature exceeding temperature of ignition of diesel fuel. Fuel is injected into cylinders where air temperature makes about + 600 °C, with some advancing and ignites itself. Thus, spark plugs for ignition of fuel are not required.

There can be a situation when at very cold engine owing to compression the necessary temperature of ignition is not reached. In this case it is necessary to make preliminary heating of the engine. In each cylinder there is a glow plug which makes heating of the combustion chamber. Duration of preheat depends on external temperature and is regulated by the control unit of the engine via the preheat relay.

The diesel engine has three various ways of injection of fuel: by means of a vortex chamber, a prechamber and direct injection.

At vikhrekamerny and prechamber injection fuel is injected into a preliminary chamber of the corresponding cylinder. Mix at once ignites. The oxygen volume which is available in a preliminary chamber is sufficient for combustion only of part of the injected fuel. The remained not burned down part of fuel pressure, arisen in the course of combustion, jumps out the combustion chamber. There fuel burns down completely.

At direct injection fuel is injected directly into the combustion chamber.

Fuel moves the toplivopodkachivayushchy pump under pressure of 3.5 atm. to the fuel pump of a high pressure (FPHP). In TNVD already at low numbers of turns the constant pressure of compression over 1300 atm is created.

Are a part of fuel system: a fuel tank, the fuel filter, nozzles, fuel tubes and hoses, the fuel reserve sensor located in a tank and the block of electronic control the engine.

Fuel moves the special pump via the filter. In the filter the dirt and water containing in fuel settles.

The engine is operated by the electronic system similar to a control system of petrol engines. The system operates operation of the engine, analyzing information arriving from a large number of sensors.

The fuel cut-off valve at switching off of ignition is absent. To kill the engine at ignition switching off, the control unit of the engine sends a signal which, in turn, stops supply of fuel to nozzles to the TNVD control unit.

The fuel system is designed so that not to allow air "suction" in the absence of fuel in a tank. The control unit constantly checks fuel level in a tank, processing information arriving from the sensor of a reserve of the fuel located in a tank. When falling a reserve of fuel to a certain level the control unit lights the warning lamp on a control panel then forcibly causes admissions of supply of fuel, limiting to that the maximum speed. It proceeds until fuel level in a tank does not exceed an admissible mark.

The fuel system of diesel engines is very reliable. When using pure fuel and performing regular service it has to function regularly before the termination of service life of the car. After very big run internal components of nozzles can wear out, and they will need to be repaired. As the pump - nozzles have a difficult design, repair is recommended to be carried out in a specialized workshop.

Security measures and rules of observance of purity during the work with fuel system

• Do not use naked flame near a workplace, do not smoke and do not hold any strongly warmed subjects. There is a danger of accident! Keep in readiness the fire extinguisher.
• Watch normal ventilation of a workplace. Fuel couples are poisonous.
• The fuel system is under pressure. When opening system fuel can escape under pressure. Collect fuel a rag. Use goggles.
• During the work with components of a power supply system of the diesel engine observe special precautionary measures. In special degree it belongs to nozzles. Keep in mind that fuel pressure at the exit makes about 1100 atmospheres of nozzles. Do not allow hit of any parts of a body under a fuel stream.
• Hose connections fasten by means of tape or tightening collars. Tightening collars need to be replaced with tape collars or collars of the last design surely. For installation of tape collars there is a special adaptation, for example HAZET 796-5.
• Carefully clear connections and the places adjoining to them before opening.
• Stack the removed details on a pure lining and close. Apply for this purpose polyethylene or paper. Do not apply for this purpose fibrous fabric!
• Carefully close open details or put technological caps if repair lasts some time.
• Establish into place only pure details. Take out spare parts from packing only just before installation. Do not apply details which were stored unpacked (for example, stored in a toolbox).
• At the opened fuel system whenever possible do not work with compressed air. Whenever possible do not move thus the car.
• Do not apply the sealants containing silicone. The silicone elements which got to the engine in the engine do not burn down and damage a lambda probe.
• Security measures at removal of a fuel tank
• Before removal of a tank merge from it fuel or pump out fuel the pump which is specially provided for this purpose.
• The fuel tank is removed from the lower party of the car. Before a detachment of collars of fastening of a tank bring to it from below a jack and linings.
• The empty tank is explosive and cannot be utilized in such look. Before utilization the tank has to be cut on part. Watch that thus there was no spark.
• After installation of a tank into place start the engine and check tightness of all connections.