computingcode

Hello,
I have and AUDI A8 D2 with an AAH engine (2.8L). I have the car for some years now, and since then it had an issue with the fuel tank. I can only drive until the tank is around half full. When I fill up It only takes around 40L (I know the tank should have 80L). If I try to fillup more it starts leaking out from behind the fill hole (under the fender). The gauge shows full when I fillup.
If I go below the half tank marker there is a risk the engine will start misfiring and stalling. Refilling fixes this. The pump was replaced a few years before I got the car....
Anybody with same symptoms, someone knoledgeble who might have an ideea how to fix this?

Help is appreciated,
Thank you.

silverd2

The tank has 2 "halves" (saddle shape tank with 2 level sensors and 1 pump) ... the fault probably lies with the installer, touchy installation to get pickups for both sides connected correctly to the fuel pump.

If it never worked for you correctly, it's probably the wrong pump with only one pickup .... if it worked correctly for you, then failed, then it was installed incorrectly.

To fix: new pump installed correctly or reinstall the old pump correctly.

Most likely the wrong pump, if it never used a full tank for you.

computingcode

It used the full tank before the replacement. How can I identify if the new pump is correct or not? Is something identifying about it from the outside (without pulling it out)? It is visible from the trunk, under a metalic cover.

computingcode

don't know how to edit so I will write here.
The car only had 2 owners, my aunt and me. That is how I know it failed right after the pump was replaced.

spitanddirt

Here you go.

Compare yours to these pictures.

https://www.audiworld.com/forums/a8-...-pics-2799219/

Mortem76

Have the same issue on my A8 D2 and my mechanic is now fixing it. It is one of the 2 issues:
- The fuel pump is dying and is not able to blow in the tank (through the scavenging pipes) at the correct pressure (4-8 bar if I recall well but I can be wrong on this number) and need to e replaced. Not really likely on your one as it has been replaced already (unless it has been replaced with a cheap one)
- The connection between the scavenging pipes and the fuel pump have not been done properly (not well aligned). It seems to be a quite common issue after fuel pump replacement
Just go to see your preferred mechanic to check it for you and - if necessary - replace it by a quality one: VDO or Bosch

silverd2

You can't see from above if the pump has two intakes on the bottom or if it was installed correctly (both intakes aligned with tank pickups).

twentysevenlitres

You are going to have to pull the pump out of the tank regardless.
If it's not seated correctly, it's going to have to be reseated.
Before reseating, you'll need to check the in-tank bottom half is correctly 'hung' from the filler pipe (it has a hook at the top which hooks over the filler inlet pipe at the top of the tank)
When it's pulled back out, you can visually inspect the pump itself (not the housing).
Correct reinsertion is critical and requires a good independent who knows what they're doing, or diy if you know what you're doing!

Most of us will only buy the Seimens VDO pump. Various suppliers, though World Impex are good. I wouldn't trust Ebay sellers to supply the right one.

Mortem76

Below is link with a list of most (all?) reference of fuel pump working with the A8 D2:
https://avs-part.com/part/audi/4D0906091C/
I would stay with official Audi/VW reference or VDO or Bosch P/N.