Audi A6 2.5 TDI: Air in Fuel Line - Fix It!

"Hello, for the past few days, I've been having a problem with air in my fuel line. When I bleed the diesel filter, the bubbles mostly disappear, but then only very tiny bubbles remain. Are these normal? I'm quite desperate. The fuel injection pump is new, as are all the fuel lines to the ESP, the diesel filter, and the fuel filter housing."
What I've also noticed is that there are a lot of bubbles coming from the return line (I've installed a section of transparent tubing).

Thank you in advance for any suggestions .

Hi,

Is there a problem when starting? I remember the engine being very sensitive to air intake before... I've already tried bleeding the system. But first, let's figure out what the actual problem is.

AudiHeiko96 wrote:

I also noticed that there are quite a few bubbles coming from the return line.

Then you've probably already found the cause.

If air is entering the reservoir (RL), it's also likely getting into the ventilation system (VL) through the "Knackfrosch" (presumably a component). Therefore, you need to find the source of the air entering the reservoir. I'm not familiar with the 2.5L engine. Is the air intake control element (AKE) still a vacuum-operated system (VEP) with an electronic sensor (ESD), or is it already a pressure-driven (PD) system? If it's still a vacuum system, I would start by replacing the breather hoses, as they are known to cause air leaks.

Greetings.
Guste.