Boost Too High AFN, No Limit.

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/Skoda/SEAT (AFN) engine with a GT1749VA turbocharger and 0.216 injectors. The EGR system has been removed. The engine control unit (ECU) software has also been tuned for this 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 adjusted. Now, there's no longer any apparent limit. According to the display, the pressure is rising up to 2 bar. Consequently, the MSG (presumably a safety device) is triggering 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 diagnosis function. It opens and closes the pressure chamber on the turbocharger. I even replaced it, as 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 also removed the line for the atmospheric pressure, but that didn't change anything either. The MSG (presumably a control module) and the boost pressure gauge are also showing very similar values. I'm slowly 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,

Yes - hello first of all .

Quote:

I'm slowly running out of potential sources of errors.

I would cautiously estimate that the VTG adjustment mechanism is stuck. This adjustment is a control unit that, as the name suggests, regulates the boost pressure, not just limits it.

Look at this: https://community.dieselschrauber.org/en/viewtopic.php?t=3004&highlight=vtg
and under "expert articles".

The problem is that it usually involves hot connections. Under certain circumstances, when the loader is stationary and has cooled down, the VTG (Variable Transmission Gear) might function.

You only need to ensure that the vacuum decreases steadily as the boost pressure increases, so that the boost pressure is regulated in a timely manner.

The easiest way to do this is with a vacuum gauge, a 2-meter hose, and two T-pieces.

1. Place a T-connector between the vacuum sensor and the measuring device.
2. Place another T-connector just before the measuring device and seal the open end with a stopper that can be easily removed.

Place the device inside the chamber and perform a test run. If the vacuum pressure continuously decreases and the boost pressure continues to rise above the target values, remove the sealing plug. If the boost pressure continues to rise further (without vacuum) ----> replace the turbocharger, or buy a decent one.

"If the MSG (Manifold Absolute Pressure) sensor trips due to exceeding the intake manifold pressure, then I have 0.0 bar of boost pressure. Based on this, my thought is that the turbocharger is mechanically sticking. I also performed the actuator diagnosis while the engine was warm. I could clearly see that the threaded rod and the eye moved approximately 1.5 cm. However, tomorrow I will connect a vacuum gauge to the control hose and see how it behaves."

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 in the forum.

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

1.) Your charger is not actually "new" or "only 3,000 km used," but rather comes from other, essentially recycled, sources.
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 ATL for a new one, ensuring an equivalent replacement.

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 (presumably a control module) registers the boost pressure without any problems. The boost pressure display and the boost pressure reading from VCDS are synchronized. Besides, this functionality was already present before. The software couldn't have rewritten itself. 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 -again- about it .

Control engineering is a very complex topic, to say the least, it's almost 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 of 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 was misaligned by approximately 1.5 cm.

1. In limp mode, the fuel injection quantity is also significantly reduced, so that there is hardly any exhaust gas flow left, with which significant boost pressures could be generated.

2. In actuator diagnostics, the maximum actuator force (full pressure or vacuum) is used: this is essentially a "hammer test," which 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 perhaps post a meaningful log here with information on target/actual boost pressure, N75 control, target/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 injection limiting?

Do you see a specific purpose in the target air mass value here?
Because this only applies to the MWB3, which is actually only relevant for issues related to AGR (Agricultural Research).
The actual intake manifold pressure (LuMa-Ist) would be more useful (as an indicator of turbocharger air leaks or restrictions in the intake passages), and that data is also available in the MWB10, along with the throttle position, ambient pressure, and again, the actual intake manifold 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 starting 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 stiff. After cleaning it, the adjustment could be easily adjusted again. I reassembled everything and took it for a test drive. During the test drive, I noticed that, in my opinion, the boost pressure control seems to be working, but it 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.