AFN Turbocharger Failure: No Boost Pressure

Hi.

It concerns the AFN engine in my neighbor's 1999/2000 A4 B5 Avant TDI.

She had been experiencing occasional limp mode issues. Today, I took it for a test drive, and the boost pressure reached a maximum of 0.7 bar, after which I heard a hissing sound coming from the engine compartment. Upon inspection, I found that an intercooler hose had cracked. A new one will be ordered on Monday.

To allow her to get back to work, I patched the tear with a patch and reinstalled the hose.

During the test drive, the AFN (air flow sensor) worked normally again. When I pressed the accelerator, a black cloud shot out from the back, it briefly accelerated, and then the turbo boost completely disappeared.

Even after restarting, no change can be achieved; the boost pressure remains completely absent. The turbine wheel of the turbocharger on the fresh air side is intact and rotates even when accelerating, the variable turbine geometry (VTG) is working freely, the charge air path is mostly tight, and there are no error entries.

Currently, I'm feeling a bit stuck and need some inspiration. I have a VAG 1551 available and would appreciate some ideas.

Thank you, Rüdi.

Quote:

...and I need some ideas

Please, take a look at this, for example: https://community.dieselschrauber.org/en/viewtopic.php?t=2992

- Is the vacuum system sealed?
- Is the VTG controlled by applying a vacuum?
- Is the intake or exhaust system free of obstructions?
- Is everything okay with the cat?

Hi!

I always do the following test there:
With the engine off, turn on the ignition.
Then, observe the support structure of the VTG.
Then, an assistant needs to start the engine and gently tap the accelerator.
Then the rod needs to move the entire distance.
It's about 1 centimeter.

Then, in principle, the turbo control system is working correctly.

Okay, I will.

Steffen G wrote:

Hi! I always do the following test there: With the engine off, turn on the ignition. Then, observe the support structure of the VTG. Then, an assistant needs to start the engine and gently tap the accelerator. Then the rod needs to move the entire distance. It's about 1 centimeter. Then, in principle, the turbo control system is working correctly. Do it.

Not always. There are serial datasets where that is not the case. If you want to test it, please do so using an actuator test.

Best regards, Rainer.

Thanks for the tips. I need to see when I can get to the car; my neighbor is sleeping, and the garage is locked. Otherwise, she'll have to drive 180 km every day until next weekend in a naturally aspirated TDI.