Boost Too High: No Limit on Audi AFN Engine?

Hello,
I have already read the technical articles, but I haven't been able to find a solution to the problem.

This is an Audi/VW vehicle with a GT1749VA turbocharger and injectors sized at 0.216. The EGR system has been removed. The engine software has also been tuned for this specific setup.
My holding pressure was 1.5 bar.
It worked fine for a while. Eventually, the boost pressure started to overshoot, reaching around 1.7 bar or so, but it was regulated. Now, there's no longer any visible limit. According to the display, the pressure is rising up to 2 bar. Consequently, the MSg (presumably a safety valve) then kicks in due to the intake manifold pressure. In VCDS, you can also see that the actual boost pressure regularly exceeds the target value.
I checked the N75 using the actuator diagnostics. It opens and closes the pressure sensor on the turbocharger. I even replaced it because I had a spare one, but the effect remains the same. I also checked the control lines for proper connections. Neither with nor without the vacuum reservoir, the boost pressure is not being limited. I've also removed the line for atmospheric pressure before, but that didn't change anything either. The MSG (presumably referring to a control module) and the boost pressure gauge are showing very similar values. Now I'm running out of potential sources of error. By the way, the turbocharger is new and has about 3000 km on it.
Have I overlooked or forgotten anything obvious?

Best regards,

[Translating...]

Ja - hallo erst mal

Quote:

Nun gehen mir langsam die Fehlerquellen aus.

Ich würde vorsichtig schätzen, die VTG Verstellung klemmt. Diese Verstellung ist eine Regeleinheit, die wie der Name schon sagt, den Ladedruck regelt, nicht nur begrenzt.

Guck mal hier: https://community.dieselschrauber.org/en/viewtopic.php?t=3004&highlight=vtg
und unter Fachartikel.

Das Problem ist, daß es sich meist um Heißklemmer handelt. Im Stand bei ausgekühltem Lader kann die VTG unter Umständen funktionieren.

Eigentlich musst du nur sicherstellen, daß der Unterdruck bei steigendem Ladedruck stetig abnimmt, damit der Ladedruck rechtzeitig eingeregelt wird.

Am einfachsten geht das mit einem Unterdruckmessgerät 2m Schlauch und 2 T-Stücke.

1. T - Stück zwischen der Unterdruckdose, 2. T - Stück kurz vor dem Messgerät plazieren und das offene Ende mit einem Stopfen verschliessen, der sich leicht entfernen lässt.

Gerät in den Innenraum legen und Probefahrt durchführen. Fällt der Unterdruck stetig ab und Ladedruck steigt über die Sollwerte hinaus weiter an, Verschlußstopfen ziehen. Steigt der Ladedruck dann (ohne Unterdruck) noch weiter an ----> Turbolader umtauschen, bzw. was Gescheites kaufen.

"If the MSG (Manifold Absolute Pressure) sensor trips due to exceeding the intake manifold pressure limit, then I have 0.0 bar of boost pressure. Based on that, my thought is that the turbocharger might be mechanically sticking. I also performed an actuator diagnosis while the engine was warm. Here, I could clearly see that the threaded rod and eye mechanism were misaligned by about 1.5 cm. However, tomorrow I will connect a vacuum gauge to the control hose and observe its behavior."

Hi Lars!

From me as well, a warm welcome in advance!

Similarly, I am not aware of any cases of VTG errors that have not already been discussed or resolved in technical articles and/or multiple times within this forum.

While Villa Bacho is still being edited, it could already be guessed by Villa Riba, consequently:

1.) Your charger is not actually "new" or only "run for 3,000 km," but rather comes from other sources – essentially, recycled ones.
2.) Your software is not compatible and/or is poorly calibrated with respect to the tolerances of the entire lighting control system.

In that case, I would logically suggest, first and foremost, restoring the original dataset or installing an unmodified version of the VAT software.
THEN, check if the error occurs in exactly the same patterns.
The next step would be to exchange the existing ATL with a new one and ensure equivalent performance.

Best regards from Munich!

My holding pressure was 1.5 bar.

'Isn't that more than just borderline with the series production boost pressure sensor?'

By the way, the charger is new and has approximately 3000 km of mileage.

New or 'new'?

The MSG registers the boost pressure without any problems. The boost pressure display and the values read by VCDS are synchronized. Besides, this functionality was already present before. The software couldn't have rewritten itself. And the turbocharger is definitely new.

Hi Lars!

Larsman wrote:

... Especially since the function was already there. The software didn't rewrite itself. ...

DieselBär30x wrote:

... and/or is poorly tuned to the tolerances of the entire LD control system. ...

Short: ...think about it -again- .

Control engineering is a very complex topic, to say the least, almost like "a science in itself!"
...even the absolute experts, or rather, the MANUFACTURERS themselves are aware of this, and that is why they are also forced (through updates to the software) to make improvements .

If you want to receive helpful assistance, please follow steps 1 and 2.
Of course, it could also be due to an unfavorable alignment of the stars, however - to be honest - the probability is extremely low.

Best regards from Munich!

Larsman wrote:

If the engine control unit (ECU) shuts down due to exceeding the intake manifold pressure, then I have boost pressure = 0.0 bar. Based on this, my thought was that the turbocharger is mechanically malfunctioning. I also performed the actuator diagnosis while the engine was warm. Here, I could clearly see how the threaded rod with the eye moved approximately 1.5 cm.

1. In limp mode, the fuel injection quantity is also greatly reduced, so there is hardly any exhaust gas flow left to generate significant boost pressures.

"In actuator diagnostics, the system operates with maximum actuation force (full pressure or vacuum), which is essentially a 'hammer test'. This makes it difficult to detect minor to moderate mechanical obstructions."
Furthermore, the turbine casing remains relatively cool during the actuator test, which means that genuine hot spots can easily go unnoticed.

Could you please provide a meaningful log with data including target and actual boost pressure, N75 control signals, target and actual air mass, injection quantity, and injection limiting?
hg
Herbert.

Herbert wrote:

Could you perhaps post a meaningful log here with the target/actual boost pressure, control of the N75 valve, target/actual air mass, injection quantity and limitation?

Do you see a specific purpose in the target air mass value here?
Because this only applies to the MWB3 system, which is primarily relevant for issues related to agricultural subsidies (AGR).
The actual intake manifold pressure value would be more useful (as an indicator of turbocharger boost leaks or restrictions in the air passages), and that data is also available in the MWB10, along with the throttle position, ambient pressure, and again, the actual charge air pressure.

In short, I would start here with an MWB8+10+11 log.

Hello everyone,

"On Saturday, I manually controlled the turbocharger using a vacuum pump. I noticed that it returned to its original position quite slowly after being adjusted. So, I quickly disassembled it. As some have already mentioned, the needle adjustment was quite dirty. This made the adjustment very difficult. After cleaning it, the adjustment could be easily changed again. I reassembled everything and took it for a test drive. During this test, I noticed that, in my opinion, the turbo boost control seems to work, but reacts rather sluggishly. However, I must say that I'm still using the old N75 valve, which I will replace on Wednesday if I have time. I also plan to do a logging run."
Thank you for the answers so far.