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, and give me some feedback.

I initially thought that each trip would be saved as a separate log, but the five trips I took were combined into a single entry.
"The last time it happened, at approximately 3000 RPM, it went into limp mode. The time before that, it also happened at a similar RPM. The last time, everything seemed to work up to 4000 RPM, but subjectively, the power felt lacking (the error memory was cleared after the limp mode)."
Error entry:
17958 - Boost pressure.
P1550 - 35-00 - Difference in regulations.

I logged in on August 3, 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, from time 8.28 seconds to the end (approximately 18 seconds), the boost pressure is too high.
It continues to rise, 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 TL unit) to the duty cycle.

I've now replaced the N75 once.
After the Popometer, it arrives a bit sooner and works a bit 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 doesn't revert to limp mode.
Looking at the duty cycle, the load pressure is again almost at 100%.

The hoses are 100% correctly connected; nothing has been swapped, and I've also compared them to the Audi wiring diagram to ensure that no one has mixed anything up.

I also once disconnected the hose from the vacuum pump and connected a vacuum pump. In this case, the entire vacuum I created, which was -0.6 bar, dropped completely within about 10-20 seconds.
The vacuum chamber is sealed, so 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 with the engine control unit?

klahaui wrote:

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

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 reassures me .
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 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 the data again today, at the same location and under the same conditions.

The result looks 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, 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 logs showing a very slight, consistent throttle position, with very gentle acceleration, around 2.0-3.0.

Okay, here's the translation:

"Just one more clarification from my side."
I disassembled and cleaned the VTG this week.
The travel distance of the lever was simply too short, with a maximum of 3mm.

Due to rust on the plate beneath 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, with only brief overshoots.

Thank you for the feedback!

klahaui wrote:

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

Rust in the VTG mechanism
I always 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-inhibiting soot could accumulate in the VTG (Variable Turbine Geometry)?

Beneath the VTG adjustment mechanism, there's a round plate, and the underside of this plate showed clear signs of rust.
I drive 30,000 km per year, so the battery's standby 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,

Are you watching: https://community.dieselschrauber.org/en/viewtopic.php?t=25869

In this case, the charger housing was deformed. And then, there was also rust.



Edit: ...but now