2.5 TDI BDG: Boost Surge Explained

Hello,

habe mal den Ladedruckaufbau gelogged (3. Gang Vollgas), weil meine VTG etwas schwergängig zu sein scheint. Der Ladedruck erreicht zwischenzeitlich fast 2.6 Bar. Is that still okay?

The engine is a 2.5 TDI BDG with 140,000 km (approximately 87,000 miles).

Thank you very much in advance.

What should I log with?

[Translating...]

VCDS Lite...

The car reminds me a lot of my experience 'back then'. Some 2.5V6 engines have this issue. Even without the front/main catalytic converter, it didn't show any improvement. Manufacturing tolerances. }

Is the dataset up-to-date? Theoretically, you can check if the VTG (variable turbine geometry) is functioning by disconnecting the vacuum pump, but I don't know if it's easy to access that part on this engine.

Best regards, Rainer.

dieselschrauber wrote:

...honestly, I'm not sure if you can easily get to that area on the engine.

It's doable with small fingers, but it won't be pretty.

How can I tell if the dataset is up-to-date?

I tried testing the VTG with a syringe. I couldn't detect any stiffness. The rod followed the movement of the syringe plunger directly. However, I'm not sure if I pushed the 60mL syringe all the way in; it probably didn't reach the very end. The vacuum seems to be okay (-700 mBar). Could it also be the N75 valve? Unfortunately, the actuator diagnosis switches abruptly between 100% and 0%, making it difficult to test properly.

I've found another peculiar entry in the log. It seems like the boost pressure regulation is oscillating correctly here. This might have been during a thrust phase. Therefore, I'm not sure if it means anything significant.

Quote:

How can I tell if the dataset is up-to-date?

By posting the VCDS control unit information and having someone check if there's an update available.

Can it be recognized from here?

Address 01: Engine Labels: 059-907-401-AKE.LBL
Controller: 8E0 907 401 T
Component: 2.5L V6 TDI G000SG 0004
Coding: 02002
Shop #: WSC 63251
VCID: 361F603F0149
00006059 130 106KC318_1.V14834812390
No fault code found.
Readiness: Not applicable.

Yes, dataset for VAG part number: 8E0 907 401 T, software version 0004.

This is probably not the latest version. But is there any way to update it other than installing a new control unit?

Your engine control unit can be normally updated via OBD by a qualified mechanic or tuner who has a current, compatible data set.

Best regards, Rainer.

Are you sure? I always find information stating that the 2.5 TDI engine control unit cannot be reflashed, and the technical service bulletins (TPIs) consistently recommend replacing the control unit as a solution.

If you have access to the TPIs, why don't you simply look for the answer yourself regarding your problem?

It's logically flashable; it's an EDC15VM+ unit.

Best regards, Rainer.

Regarding this specific problem, I haven't found anything concrete. However, with other issues (e.g., idling problems) in the BDG engine, the control unit is sometimes replaced due to a software update.

Okay, it's possible that the control unit has a fundamental hardware problem that cannot be fixed by changing the software.
I can't really think of any specific reason related to the boost pressure control for that.

Just try replacing the N75 valve; it's not expensive and rarely causes any issues.

Best regards, Rainer.