2003 AUDI A8 fuel type

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The fuel is conveyed via the filler pipe into the
right tank chamber (as viewed in direction of
travel). The fuel passes via an additional
overflow channel at the end of the filler pipe
predominantly into the right pump reservoir.
Use of the small overflow channel ensures
that even small quantities of fuel (e.g. filling
from canister) pass directly into the pump
reservoir.
The breather function for the side
compartments is provided by two breather
pipes to the main chamber.Routing the filler pipe beneath the
longitudinal member means that the lowest
point of the pipe is not at the connection to
the fuel tank, thus producing a siphon effect.
A residual quantity of fuel remains in the filler
pipe. This necessitates a separate pipe to the
filler neck for the main chamber breather
function and for OBD II leakage diagnosis.
When the tank is full, the filler hose is closed
by a float-type shutoff valve at the end of the
filler pipe. Interior of fuel tank (filling)
SSP282_006
Baffle housing
of expansion tankReservoir
with pump unit, left Reservoir
with pump unit, rightFloat-type shutoff valve
Breather pipe
to filler pipe
Overflow channel Filler pipe

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Engine, Mechanics
Function
The main functions of the float-type rollover
valve are as follows:
– Closing-off of pipe to filler neck in the
event of rollover
– Closing in dynamic driving mode
– Closing by rising of float in valve in the
event of a brief excess of fuel in the tank
due to sloshing
Closing-off of the pipe to the activated
charcoal filter stops fuel overflowing into it. Expansion tank
The expansion tank (capacity approx. 2 litres)
consists of a plastic housing clipped to the
upper shell of the tank.
The internal expansion tank houses a float-
type rollover valve and a small suction jet
pump which constantly pumps the tank empty
whilst driving.
SSP282_009
Inlet pipe
from tank filler neck
Float-type
rollover valve
Float-type shutoff valve Breather pipe
Suction jet pump
intake connection

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The reservoirs with pumps and immersion
tube senders rest on and are clipped to the
bottom of the tank. Flanged covers provide
access to the components.
Single-stage pumps are used for diesel
engines (Common Rail). On account of the
higher viscosity of diesel fuel, pre-delivery
(extraction from bottom of tank) is not
implemented by way of separate pump units,
but rather by suction jet pumps. Two-stage fuel pumps
The two fuel pumps (petrol engine) are of the
two-stage flow type.
The first stage (pre-stage) pump unit draws in
fuel from the bottom of the tank and conveys
it into the reservoir. This ensures that even
small residual quantities can be transported.
The second stage (main stage) pump unit
draws in fuel directly from the reservoir.
SSP282_003
Main stage delivery end
Main stage suction end
Main stage
pump unit
Pre-stage
pump unit
Pre-stage suction end
Fuel tank
Main stage suction end Pre-stage delivery endReservoirOverflow Return