Electric fuel pump (Audi 100 C4)

The fuel pump is mounted on the underside of the fuel tank. A relay supplies voltage to the pump. A safety switch is installed to ensure that the pump only supplies fuel when the engine is running.

Checking the fuel pump

If the pump is not working properly or it is suspected that the fuel supply is insufficient, some operations can be carried out to check the pump operation. Some experience with electrical equipment is also necessary. It is assumed that the corresponding fuse is OK. This is fuse #17 in the fuse box.

To check the main pump activation, you need to raise the rear of the car, support it on stands and listen near the fuel tank to see if the fuel pump clicks when an assistant turns on the ignition. If it does, determine where the fuel is remaining.

Place a rag under the threaded connection of the fuel lines and loosen the connection. If fuel sprays out, this is a sign that the fuel system is under pressure. If this is not the case, then turn on the starter. Now the fuel should spray out. If this does not happen:



Remove the boot floor trim and unscrew the black cover. Remove the multi-pin plug and check with a test lamp or voltmeter whether there is voltage between the two contacts, i.e. those to which the brown and yellow/green wires are connected. To do this, turn on the starter. The described check shows that voltage is supplied to the pump. If there is no voltage, it can be assumed that the pump needs to be replaced.

Before replacing the pump, you need to check the pump relay.

Replacing the fuel pump

The fuel pump is specially reinforced and a special key (3307) is required to remove it. If this key is available, the pump is removed together with the inner part of the fuel intake housing.

Caution: The fuel tank may be no more than ⅔ full at the time the pump needs to be removed.

Fold back the trunk floor trim and remove the black metal cover (arrows).



Remove the multi-pin plug and the fuel return line, as well as the fuel supply line from the pump.

Now unscrew the fuel tank connecting flange. Usually a special key (2) is used for this.



The plastic union nut has small ribs through which you can insert a screwdriver (best of all is a blunt one). By lightly tapping the screwdriver, you can loosen the nut.



Now pull the connecting flange upwards.

Remove the return fuel line from the inside of the flange. Loosen the clamp and pull the fuel line down.

Remove the fuel tank sensor plug.



The above special device (1) is now inserted through the opening in the tank and into the inner part of the fuel intake housing (2). Now turn the inner part of the housing approximately 15° to the left, almost to the stop, to release the pump.



Now you can lift the pump with the inner part outward together with the connecting flange. Before removing the pump, be sure to remember or mark the exact position of the pump installation, the method of connecting the hoses and wires, so that you can then install them in the same position. After making marks and disconnecting the fuel supply line, you can remove the pump from the inner part of the fuel intake housing. This operation depends on the diameter of the pump.



If the pump (1) has a diameter of 6 mm, turn the mesh at the bottom of the inner part of the housing (3) for fuel intake to the left and pull out the pump. When installing, push the protrusion (2) on the side of the pump into the groove. Do not forget about the gasket.

If the pump has a diameter of 4 mm, then squeeze the retaining clip on the upper side of the inner part of the fuel intake housing and pull out the pump. The pump can only be installed in one position.



The pump is installed in the reverse order of removal. Pay attention to the relative position of the pump and the connecting flange, as well as the correct position of the sensor wire in the fuel tank.

For 2WD vehicles, install the connecting flange as shown on the right side of the figure and connect the hose as shown. The electrical wire for the fuel tank sensor must be routed between the fuel return line and the fuel tank.

For 4WD (Quattro) vehicles, the connection flange should be positioned as shown on the left side of the picture. The fuel tank sensor wire runs between the pump and the fuel tank.



Install the pump. The corresponding marks (arrows) must coincide with the large arrow on the outside (3).

Secure the inner part with the special key mentioned above.

When installing the connecting flange, pay attention to the installation position. The flange is marked with the symbols "QUATTRO" and "FRONT". "FRONT" in this case, it denotes models with a 2-wheel drive at the front. Both versions have an arrow that should match the arrow on the outside. Moisten the sealing ring of the connecting flange with gasoline before installation.



The original version of the article is posted on the website AUDImanual.ru