- cars with four-cylinder engines: 7.8-10.3 liters;
- cars with five-cylinder engines: 8.5-13 liters;
- cars with six-cylinder engines: 8.1-12.3 liters.
A full tank of vehicles with a diesel engine is enough for a run of more than 1000 km.
The fuel tank capacity of the AUDI 80 is approx. 66 litres, while the quattro models have a capacity of approx. The fuel tank is located under the bottom. It is made of plastic and has a very bizarre shape, especially for quattro models (see illustration 1.0).
This shape of the tank, on the one hand, is due to the desire to ensure the maximum capacity of the trunk, and on the other hand, to use the slightest free space to maintain sufficient fuel tank capacity. The problem of taking fuel from such a tank is also solved accordingly. AUDI uses a suction jet pump, which, in addition to the fuel from the tank, simultaneously captures the fuel coming from the fuel return line back to the tank. In addition, a hose is connected to the filler neck of the fuel tank, which goes to the place of the main fuel intake by the pump. When refueling even a small amount of fuel, thanks to the hose, it remains in the place of the main intake.
Attention! Before starting any work on the fuel system, you must disconnect the wire terminal «masses» (-) from the battery.
Fuel tank - ventilation
The ventilation of the fuel tank is extremely important for the functioning of the fuel system. Directly behind the filler neck is the fuel tank vent tube. A shut-off valve is attached to this tube to prevent fuel from flowing out by gravity through the vent. This valve closes the vent when the vehicle is tilted at an angle greater than 45°. In the event of an accident, this valve prevents fuel from escaping. From the shut-off valve comes a hose connected to the canister of the evaporative emission system, which is a tank with activated carbon, located at the rear of the wheel arch of the right front wheel. The accumulated fuel in the adsorber subsequently enters the fuel system (see illustrations 1.0a, 1.0b, 1.0c).
Diesel engines do not need an EVAP system.
In addition, there is an equalizing valve on the fuel tank, which, when refueling, opens the equalizing chamber of the tank connected to the filler neck (see illustration 1.0g).
The equalizing chamber of a tank is in a wheel niche of a back right wheel. While driving, as the amount of fuel in the tank decreases, the valve lets air in, thus equalizing the pressure (see illustration 1.0e).
«Devastation» the fuel tank of a diesel vehicle can have certain consequences for the engine, especially when starting it. The air trapped in the fuel lines does not interfere with the fuel supply by the pump. A similar problem occurs if air enters the system when changing the fuel filter.
TD engines. To start such an engine with air in the system, you will have to work the starter for several minutes.
TDI engines. Pumping the fuel system of these engines is quite problematic. There is a pressure reducing valve on the connecting pipe of the fuel return line on top of the injection pump, which allows fuel to be removed only at a pressure of 4 bar. The pump is not able to create this pressure as long as there is air in the system. At the same time, the pump cannot pump out the trapped air and start supplying fuel. The way out of this situation is the following.
1. Loosen the fuel return pipe fitting two turns.
2. Operate a starter until from under not densely adjoining branch pipe the exit of diesel fuel without air bubbles begins.
3. Tighten the connecting pipe.
4. Turn on the starter and start the engine.
All types of diesel engines. When pumping the fuel system, the heating of the fuel, carried out by the heating unit on the fuel filter, also presents a hindrance. The fuel heating system functions in such a way that that part of the heated fuel coming back to the fuel tank is taken by the injection pump and mixed with the unheated fuel supplied to the system. Fuel heating is carried out at air temperatures below +15°С. Due to the fact that during pumping there is air in the return fuel line, it, together with the fuel, is re-injected back into the system. The way out is the following.
5. Disconnect for a while (if the air temperature is low) the fuel supply line from the fuel filter and connect it to the pump so that fuel bypasses the filter.
6. Connect the fuel supply line to the fuel filter after starting the engine (see illustration).
Attention! Do not confuse the connecting pipes for the return and supply fuel lines installed on the high-pressure fuel pump. The letters are embossed on the end of the fuel return pipe for TD engines «OUT» («back»), In addition, the fuel return pipe has a smaller inner diameter. The fuel return pipe head for TDI engines has an unusual shape.
Cleanliness is the main requirement when working on the fuel system. All fuel lines on which repair work is being carried out must be cleaned beforehand. Do not forget that hoses and pipes are designed for pressures above 5 bar. Structurally, they are made of materials that can withstand high pressure. At the joints, they are fastened with nuts or clamps. After removing the clamps, the fuel hoses are removed by turning them on the connecting fittings. If it is not possible to remove the hose in this way, then use a wrench and remove the hose. When connecting, secure the hoses with screw clamps.
With regard to vehicles with five-cylinder engines and KE-III-Jetronic fuel injection system, it must be taken into account that the fuel system is under pressure for a long time after the engine has been switched off.
Always have a rag handy when disconnecting the fuel line to prevent fuel from spilling or getting into your eyes.
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