Wastegate: AFB or VTG?

Hello everyone!

Please don't hit me...!!!
I always think that the AFB has a VTG!
I always thought that the turbocharger also had a kind of wastegate to release excess pressure. But as I read in another post, a VTG (Variable Turbine Geometry) turbocharger doesn't have anything like that at all.
'I'm now very curious about the noise my AFB makes when accelerating. In a previous post, I described how the turbocharger builds boost in a somewhat unusual way. At an engine speed of around 2200 RPM, there's a sudden, noticeable increase in acceleration (almost like flipping a switch). At least, there's a brief, perceptible jerk in the lower gears. Simultaneously, a short hissing sound can be heard coming from the engine compartment. I've always interpreted this hissing as the sound of excess boost being released. However, if it's a VTG (Variable Turbine Geometry) turbocharger, that can't be the cause...'
I had already discussed this whole topic in an old post (with a diagram) https://community.dieselschrauber.org/en/viewtopic.php?t=797&highlight=afb+wastegate. But it didn't come out clearly whether it was a VTG or a wastegate...

Hi,

I've never dealt with wastegate chargers before, but if I'm not mistaken, they don't vent intercooled air; instead, exhaust gases are diverted around the turbocharger – see also the hose diagrams for the various models.

Are you sure your intercooler pipes are sealed?

Best regards,

Jan.

Hi Garfield,
I'm quite sure that your car has a VTG turbocharger installed.
The pressure chamber, as is the case with the AFN model, is located between the impeller blades.
She sits on the side at 1Z and Co.

Best regards, Rudi.

Hi Garfield,
I'm quite sure that your car has a VTG turbocharger installed.
The pressure chamber, as is the case with the AFN model, is located between the impeller blades.
She sits on the side at 1Z and Co.

Greetings Rudi.

Hello Rudi!

I thought the same thing (because of the strut and the pressure vessel). But in the older post (link at the top), Jan6K said that turbochargers with a wastegate can also have such a vessel and strut.
That's why I'm so unsure...

DENNIS

Hi Garfield,
Let's see how the attachment function works .
The wastegate turbocharger also has a canister with linkage, but it looks completely different.

Best regards, Rudi.

The AFB definitely does not have a wastegate turbocharger. It has a variable turbine geometry (VTG) turbocharger. The noise can be explained as follows:
When accelerating, the maximum boost pressure of the turbocharger is reached just above approximately 2000 RPM. Since the boost pressure must not increase further despite the increasing engine speed, the boost pressure is regulated or limited by the pressure control valve. This regulation process, which occurs at approximately 2200 RPM, is accompanied by a slight pneumatic noise that is audible for a maximum of two seconds. The noise, which can vary in frequency between a hissing and a scraping sound, is often mistakenly attributed to the automatic transmission.

A friend of mine had the same symptoms, including the 'switch-like' behavior. Additionally, his turbocharger engaged late, at 2200 RPM, because he has a 4-cylinder engine. He also experienced a whistling sound around 2200 RPM.
We then went to the workshop and replaced the mass airflow sensor (MAF sensor), and since then the problem has been gone, seemingly including the noise...

Andreas.

A friend of mine also had the same symptoms, namely the 'switch-effect'. Additionally, in his case, the turbo engaged too late, at 2200 RPM, because he has a 4-cylinder engine. He also had a hissing sound around 2200 RPM.
We then went to the workshop and replaced the mass airflow sensor (MAF sensor), and since then, the problem has been gone, and apparently, so has the noise...

Andreas

Hello Andreas, Hello vikinger!

I've also suspected for a while that the LMM (likely referring to a Mass Air Flow sensor) might be faulty. However, the values it's providing don't really seem to be outside the normal range. Instead, the air mass readings tend to be at the lower limit of the expected range, which shouldn't really cause such a 'switching effect' (likely referring to an abrupt change in engine behavior).

The hissing sound is a brief moment when the 'switch' is flipped, and it sounds like air is being released with overpressure for about 0.5 seconds. It's difficult to describe, and you can only hear it if you have the window open while driving. Regarding this 'switch effect,' Audi simply said: 'it must be like that.'

Regards,

DENNIS