Troubleshooting the fuel pump
Check the fuse first (chapter «Body electrical system»).
If he's okay, you need to look further.
Sometimes it is possible to determine by listening whether the fuel pump is working: listen under the car at the height of the fuel tank, whether the fuel pump turns on, while the assistant turns on the ignition.
If you hear a running sound, then the pump is probably good. If nothing was heard, you should check if the fuel is coming in:
Left: A special tool is needed to remove the fuel pump (1), which rotates the inside of the fuel intake housing (2) a little to the left. The tool must hit with its paws (arrows) into recesses on the inside.
Right: for fuel pump installation (1) with the inside of the fuel intake housing (2) to the outside (3) the correct installation position must be observed: the mark on the inside of the fuel intake housing must be opposite the mark on the outside (arrows).
Models with 6-cylinder engine and 4-cylinder engine with Mono-Motronic or Digifant injection system: disconnect the pipe leading to the fuel mixture preparation unit at the union connection. Put an extension cord on the hose coming from the fuel tank and lower its end into some container.
The assistant should turn on the starter at this time. Now fuel should flow.
Fuel filter (1) in all engine models, the Audi-100 is located on the right rear in the engine compartment. In the 6-cylinder engine shown here, the solenoid valve for the activated charcoal reservoir is located right next to it (2).
Models with 4-cylinder engine and KE-Motronic injection system and with 5-cylinder engine and KE-III-Jetronic injection system: Loosen the screw connection on the fuel supply line - keep a rag ready to clean up spilled gasoline.
Even with the engine off, some gasoline should come out now because the fuel supply system is pressurized by the fuel accumulator.
If nothing appears, the assistant should turn on the starter.
The fuel pump should now start pumping gasoline.
All models: if the pump is not working, check the multi-pin plug at the top of the fuel tank guard to see if the pump is receiving power:
Unscrew the luggage compartment carpet.
Remove the black metal cover.
Remove the multi-pin plug.
Check with a voltmeter or test lamp whether there is a (brown and yellow-green wires) voltage of approximately 12 V. For measurement, it is necessary that the assistant turns on the starter (gear lever in neutral position, vehicle on parking brake).
If the pump does not work despite the power supply, then it is faulty.
If there is no power, then the pump relay in the central switch comes under suspicion. Its verification is described in the chapter «Body electrical system».
Other causes may be: defective wiring to the relay or pump, clogged or kinked fuel line hose, clogged prefilter or fuel accumulator.
Removing the fuel pump
This already applies to the kind of work that the workshop has to do, because the fuel pump is removed together with the inside of the fuel inlet housing, and it can only be removed from the outside of the fuel inlet using a special key 3214. Anyone who can rent such a key must act as follows:
Remove the fuel sensor.
Install special key 3214 on the inside of the fuel intake housing and turn it to the left until it stops.
Remove the fuel pump with the inner part and with the fuel gauge from the tank.
remember exactly (Mark) installation position of the pump, pipes, wires and wire bands, because during installation all the elements must be assembled again in exactly the same order.
After disconnecting the pressure line, you can disconnect the fuel pump from the inside of the fuel intake housing. Depending on the pump variant:
Option I: turn to the left the grid located at the bottom on the inside of the fuel intake housing, remove the fuel pump. When installing, the lug on the side of the pump must fit into the groove. Watch the sealing ring.
Option II: squeeze the locking bracket at the top on the inside of the fuel intake housing, remove the pump. When installed, the pump can only be installed in one position.
The pump can be reinstalled on the outside of the fuel tank pickup housing.
The marking on the outer side of the case must be opposite the single notch (marks) on the inside.
Tighten the inner part again with spanner 3214. Install the rest of the parts.
Observe the installation position of the fuel sensor (as will be described below).
Fuel filter replacement
The fuel filter in the Audi-100 is of such a size that it does not need to be changed during the life of the engine. Replacement of the fuel filter can only be advised if there is a malfunction in the fuel filter or when installing a new engine.
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