Audi A4

since 1994 release

Manual of the car

Audi A4
+ Running gear
+ Regular servicing
+ Engines
+ Turbo-supercharging
+ System of an exhaust
+ Cooling system
- Fuel tank and fuel pump
   For what ventilation of the fuel tank is necessary?
   The fuel level indicator sensor in the fuel tank
   Fuel-supply lines
   The fuel pump with the electric drive
   Dismantle of the petrol pump with the electric drive
   Replacement of the fuel filter
+ Air filter and channels of absorption
+ System of injection
+ Coupling
+ Transmission and main transfer
+ Suspension bracket of wheels and steering
+ Brakes
+ Wheels and tires
+ Electrotechnical equipment
+ System of ignition
+ Lighting
+ Alarm equipment
+ Tools and devices
+ Heating and ventilation
+ Body details
+ Salon
Search of malfunctions
Technical characteristics


For what ventilation of the fuel tank is necessary?

The electromagnetic valve of the coal filter is at the left below behind in a motive compartment

1 – a tube to the coal filter;
2 – electromagnetic valve;

3 – electric connection;
4 – a tube to an inlet collector of the engine.

The coal filter (2) is behind in the right forward wheel niche. Further are visible: a tube to the electromagnetic valve (1), a tube to ventilation of the fuel tank (3).

Ventilation of the fuel tank is important for faultless supply of fuel: in that volume in what fuel is spent, air has to get into the fuel tank, otherwise in the fuel tank the lowered pressure is formed, and supply of fuel will stop.

Further the fuel tank has to be ventilated in order that fuel had an opportunity for expansion when heating. At the gulf of fuel from the fuel tank enough air has to be forced out in order that the filled-in fuel did not pour out through a jellied branch pipe.

Ventilation of the fuel tank in Audi A4

  • Above in the fuel tank the ventilating tube is connected. In the beginning it goes through connecting knot on a jellied branch pipe to the so-called gravitational valve. It closes a tube as soon as the car bends sideways more than on 45 °. In such a way fuel pouring out through a ventilating tube at accidents is not allowed.
  • From there the ventilating tube is removed not just outside, and enters the coal filter in the right forward wheel niche. The purpose of such device consists in catching of the fuel vapors, harmful to the environment, acting through this tube (arising, for example, due to heating of contents of the fuel tank). When the engine works, at a certain load of it gases are again sucked away from the coal filter. When it occurs, defines the electromagnetic valve operated by fuel injection.
  • Parallel to this system there is a high-speed ventilation which conducts to a jellied branch pipe through the compensating volume in the form of the capacity of a special purpose in the jellied mine of the fuel tank. This way of ventilation matters, first of all when filling when fuel level quickly rises, and fuel vapors have to be forced out, but so that not to get to the atmosphere in too large number.
  • During the movement the same way to the fuel tank atmospheric air according to the spent fuel therefore in the fuel tank the lowered pressure cannot be formed gets.