A6 AYM Power Loss: Causes & Solutions

Hello everyone!

A good friend has owned an Audi A6 with the engine code AYM (V6 155 hp) since a few months ago. The car was manufactured in 2002.
The engine's performance isn't quite optimal, so we recorded some data logs yesterday. We logged the data while running in 3rd gear, with the engine speed ranging from 1000 to 4500 RPM.
I'm a little out of practice, so I'm hoping for some support .

What I noticed about it is:
1.) Mass Air Flow Sensor (MAF): In many operating ranges, the amount of fuel injected is limited by the air mass, even when the target boost pressure is reached. It appears the MAF sensor is somewhat aged, so we will replace it.
2.) Turbocharger pressure regulation: The overboost of 400 mbar startled me a bit. The target turbocharger pressure (TV) is constantly being lowered by the engine management system (MSG), seemingly without any effect, until the turbocharger pressure suddenly drops. Is this a sign of a stuck variable geometry turbocharger (VTG)?

Best regards, Wolfi.

wolfi_b wrote:

Boost pressure regulation: the overshoot of 400 mbar startled me a bit. The TV (turbocharger) is being continuously reduced by the MSG (manifold pressure sensor), seemingly without reaction, until the boost pressure suddenly decreases. Is this a sign of a stuck VTG (variable turbine geometry)?

Yes, usually .
Besides the VTG (Variable Turbine Geometry), the magnetic valve could also get stuck, which essentially leads to the same result.

"That's completely wrong. The engine speed would have been fine, but the air mass is all wrong. You can't expect any boost if the exhaust flow doesn't match the pre-programmed control map."

What do the side effects look like?

I hadn't even thought about the pre-tax identification field. We'll try replacing the mass airflow sensor and then see what the boost pressure control does.
I'll take a look at the camshafts first, but the power delivery and smoothness of operation are unremarkable.

The speed is "strictly monotonically increasing" from 1000-4300 RPM. In the following diagrams, this is

@Christian:
Could you perhaps post a boost pressure log from your AKN engine? I would like to see how the turbocharger (TV) and boost pressure behave in a functioning V6 engine.

Best regards, Wolfgang.

Okay, I understand. Please provide the German text you want me to translate.

Hello,

I still owe you the solution.

First, the mass airflow sensor (MAF) was replaced, and the fuel injection volumes were then back to normal, but the turbocharger boost pressure remained unchanged.
A trial replacement of the N75 valve didn't make any difference either.


So, I cleaned the VTG after all...

... and behold: the build-up of boost pressure is correct .

Thank you for your help.
Best regards, Wolfgang.