Audi A3 8L: Engine Performance Issues & Limp Mode

Today I did a logging trip with my A3 (AHF 110hp) because the power doesn't really kick in until around 2100 RPM.

"Over the past few days, I pressure-tested the entire charge air system at 1.5 bar, and everything was leak-free. Additionally, the VTG (variable turbine geometry) was inspected and found to be operating smoothly, and all vacuum hoses have been replaced."
AGR has been locked for testing purposes.

I have to admit that I can't make sense of my log because there is simply too much information.
I hope someone can help me with editing this, perhaps explain it to me once, and give me some feedback on it.

I initially thought that each trip would be saved as a separate log entry, but the five trips I took were combined into a single entry.
The last time it happened at approximately 3000 RPM, the engine went into limp mode. The previous time, everything worked up to 4000 RPM, but subjectively, there was a lack of power (the error memory was cleared after the limp mode event).
Error entry:
17958 - Boost pressure.
P1550 - 35-00 - Difference in setpoints.

I logged in on August 3rd, 2011.

I hope this is somewhat appropriate; I haven't really had much experience with this before.

Thank you very much.

In the last log entry, from time 8.28 seconds to the end (approximately 18 seconds), there is excessive boost pressure.
It continues to rise steadily, although the aspect ratio of the N75 works against it.

I guessed that either the pressure sensor (N75) is malfunctioning or the variable turbo geometry (VTG) is stuck.

Is the hose connection correct – are any connections reversed?

The easiest way to determine if the vacuum pressure drops as the duty cycle increases is to compare the actual vacuum pressure (measured with a vacuum gauge and a T-connector directly connected to the ballast) to the desired duty cycle.

I've now replaced the N75 once.
After the Popometer, it arrives a bit sooner and works somewhat better.

In the new log, I can also see something that surprises me: the boost pressure is about 0.3 bar too high, but it's not triggering the limp-home mode again.
Looking at the duty cycle, it's almost back to 100% with this charging pressure.

The hoses are connected correctly; nothing has been swapped around, and I've also compared the connections to the Audi wiring diagram to make sure no one has mixed anything up.

I also once disconnected the hose from the vacuum pump and connected a different vacuum pump. In this case, the entire vacuum I generated, which was approximately -0.6 bar, dropped within about 10-20 seconds.
The vacuum chamber is sealed; nothing is falling off.
However, I suspect that the hose connected to the fresh air intake on the air filter housing is blocking the pressure. When I release it, the pressure gauge momentarily stabilizes and then continues to drop.

Could it be possible that the previous owner had something messed up in the engine control unit (ECU)?

klahaui wrote:

Could it be possible that the previous owner had something messed up in the engine control unit (ECU)?

Due to the injection volumes being relatively low, it would already require extreme negligence. The VTG (likely referring to a specific component) will be difficult to operate.

Best regards, Rainer.

That already makes me feel better .
Is there anything else that stands out?

It's difficult to access the turbo from above, and I can't set up my lift again until April.

I will keep an eye on it and I will definitely check the VTG again.

Thank you.

After driving 500 km on the highway with short bursts of full acceleration and speeds ranging from 120-180 km/h, I logged data again today at the same location under the same conditions.

The results are looking a bit better now, and the boost pressure should be within the acceptable range.

Despite everything, I will disassemble the VTG and verschandeln it thoroughly.

It looks better now, but you won't be able to detect slight misfires with full throttle and high exhaust gas flow.
More interesting than the full-throttle logs would be a very slight, yet consistent, gas pedal position with extremely gentle acceleration, around 2.0 - 3.0%.

Let's clear up another misunderstanding on my part.
I disassembled and cleaned the VTG this week.
The lever travel was simply too short, with a maximum of only 3mm.

Due to rust on the plate under the VTG (Variable Transmission Gear), it was almost completely blocked.
Since the repair today, it's working perfectly again in all areas, and the boost pressure is being regulated to just under 2 bar after brief overshoots.

Thank you for the feedback!

klahaui wrote:

The lever travel was simply too short, with a maximum of only 3 mm. Due to rust on the plate under the VTG, it was almost completely blocked.

Rust in the VTG mechanism
I previously thought that the ubiquitous soot would prevent something like that from happening.
Does your engine/supercharger have any unusual history, such as long periods of inactivity before enough corrosion protection deposits could form in the VTG (variable turbine geometry)?

Beneath the VTG adjustment mechanism, there's a round plate, and this plate showed clear signs of rust on its underside.
I drive approximately 30,000 km per year, so the battery's idle time is practically zero.
I can't say what the previous owner did, as I bought it two years ago with 200,000 km on the odometer.

I have carefully sanded this plate flat and removed the soot. All the adjustment flaps were very easy to move, and in my opinion, they were being blocked by the plate.

Best regards,

[Translating...]

Guckst du : https://community.dieselschrauber.org/en/viewtopic.php?t=25869

In dem Fall war das Ladergehäuse verzogen. Und dann plus Rost......



Edit: ..aber jetzt