Mechanics

FUEL DELIVERY

2001 Audi A8

Engine Mechanical problem
2001 Audi A8 V8 Four Wheel Drive Automatic 120000 miles

I have had this car for 5 years (great car !) Only system failure was a thermostate eveything else has been normal maintenance. Recently I tried to start the car and for the first time she did not start first time, I tried again and after a little hesitation she started, this has continued for a week now and I have changed the fuel filter to no avail. What do you think the possibilities are? Apart from this she runs lovely, thanks Aongus.
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Angy8
March 12, 2010.



Hello .. thanks for the donation .. much appreciated

Fuel supply and pressure testing is best left to qualified technicians with the correct tools on this vehicle !

Fuel supply system, function

The fuel tank employs a multichamber system.
The dual-stage electric fuel pump is located in a baffle housing (not shown in illustration).
The first stage of the fuel pump produces a stream of fuel (large arrow in illustration) which is directed to the three suction jet pumps -2-, -3- and -5-, where it is passed through a nozzle and thus accelerated. The accelerated jet of fuel draws off the surrounding fuel in the individual chambers and delivers it to the adapter plate -1- in the baffle housing via a system of lines.
The second stage of the electric fuel pump delivers the fuel from the baffle housing to the engine.
The first stage of the electric fuel pump, the system of suction jet pumps and the baffle housing together form a closed circuit inside the fuel tank.
For reliable starting, there must be fuel in the baffle housing at all times. To ensure that this is the case, even when an empty tank is topped off with a small quantity of fuel, the fuel filler pipe -4- goes directly into the adapter plate -1- on the baffle housing. In this way the fuel is always supplied directly to the fuel delivery module.
Fig. 19: Identifying Fuel Supply System Function
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Fuel pump delivery volume, checking
WARNING:Fire hazard. DO NOT smoke or work near heaters of have anything in the area that can ignite fuel.

VAG1348/3A with VAG1348/3-2
VAG1318/10
VAG1318/14
Measuring container (fuel-resistant)
Requirements for test:
Battery voltage not less than 12 V
Fuel filter OK
Ignition switched off
Test sequence
Remove floor matt at front of passenger's footwell.
Unscrew knurled nut -1-.
Remove trim -2- (-3- not installed)

Remove fuse No. S1 from fuse holder ST4 in fuse box. ST4 - blue fuse holder
Connect VAG1348/3A remote control with VAG1348/3-2 adapter cable to lower terminal of socket for fuse No. S1 in fuse carrier ST4 -arrow 1-.
Connect clamp to battery (B+) supply (for example, socket of 60 A fuse -arrow 2- at top of fuse box).
Remove engine cover panel.
Disconnect fuel return hose at fuel pressure regulator.
WARNING:Fuel system is under pressure. Before opening the system place a cloth around the connection. Then release pressure by carefully loosening the connection.
Fire hazard. DO NOT smoke or work near heaters of have anything in the area that can ignite fuel

Connect test hose -arrow- and hold end of hose in measuring container.
Operate remote control for 15 seconds (keep button pressed).
Compare the quantity of fuel delivered with specification.
*) Minimum delivery cm3 /15 seconds
**) Voltage at fuel pump with engine stationary and pump running (approx. 2 volts less than battery voltage).
Attach return hose and secure with new hose clamp.

Dave H
Mar 12, 2010.