AFN Power Loss: Causes and Solutions

Hello.
'I've been experiencing the following problem since yesterday, and I already visited the VAG workshop regarding this issue.'

- Power loss (feels like a vacuum cleaner with 50 horsepower), but it's also extremely reluctant to rev, even in the lower gears.

- Dark smoke when I give it full throttle while stationary and try to rev the engine to 4000 RPM.

- Immediately after starting, the engine revs to 2000 RPM and then drops to 860 RPM (which is normal).

- The engine is getting much hotter than usual (this isn't my imagination).


At VAG today, diagnoses were performed with the following results (75 minutes):

No error entries related to this topic!

Boost pressure is OK (with LOG data).

The pump adjustment (both at standstill and in operation) is working.

Boost pressure test completed. OK.

The pressure transducer clicked during the diagnostic test, and the pump connected to the TurboDose system was used to verify the ease of adjustment. Everything is okay (i.o.).

The measured air mass flow rate (LMM) was slightly too low (around 850, if I remember correctly). However, when using the diode trick (=good LMM), the same error pattern appeared, which leads me to believe that the LMM sensor itself is not the problem.

Workshop suggests checking the mass airflow sensor (MAF), then the catalytic converter.

Now the question:
My research in this forum suggested that over-revving could be caused by a faulty N75 valve (pressure sensor), but the workshop ruled this out.

Does the over-revving manifest as a result of a faulty catalytic converter (which blocks the exhaust system, but doesn't produce a rattling noise)?

Somewhere, I remember reading that a fuel shut-off valve might be the problem, but I can't recall where.

The workshop suggested removing the catalytic converter and inspecting it.


I look forward to hearing from you!

AfnFahrer wrote:

Immediately after starting, the engine revs up to 2000 RPM and then drops to 860 RPM (normal)

.
It sounds like there might be a faulty temperature sensor. Has it been checked before?

No.
I always thought that this issue (loss of power due to faulty temperature sensors) mainly affected PD TDI engines. But unfortunately, I'm not very knowledgeable about it.

At least the diagnostic program ran successfully. Wouldn't an implausible signal from a sensor have been detected?

The fact is that it wasn't specifically checked.

EDIT:

Ich werde mich mal um den Temperaturfühler kümmern. VThank you very much.
Sure, here's the translation:

'One more question:'

I'm sorry, but I cannot provide a translation without the actual text to translate. The provided URL appears to be a link to a forum post, but I need the content of that post to accurately translate it into English. Please provide the text from the linked page.

Up there (second part), it's just a high-speed rotation with a flashing heating element, right?
Just to rule out everything else...

I remember seeing an error code 109 on the monitor. However, according to the technician, everything was okay.

Current status:

Resistance values of the sensor after 15 minutes of driving in the following weather conditions:

Approximately 500 ohms.
Approximately 1 kΩ.

Attempt: Starting and driving the vehicle with the connector disconnected.

The engine takes longer to reach its operating speed when starting, and now it slowly decreases from that initial speed to the normal idle speed.
I assume the donor is functioning correctly, as indicated by the resistance values.

Remarkable:

The oil is leaking out of the turbocharger's oil line much more than usual.
My theory: It's likely the catalytic converter that's faulty. The high back pressure is forcing the oil out.

When my oxygen concentrator was malfunctioning, it was quite noticeable.

The car ran normally up to approximately 3000 RPM, but after that, the maximum speed was limited to around 120 km/h, and overall performance was quite poor.

After restarting the engine and everything seemed to be working again, it reached 3000 RPM.

The catalytic converter was completely broken and had deteriorated due to high exhaust gas temperatures.

Thank you for the information.

'Even after a restart, the performance on mine is still bad. Otherwise, it only revs up to just below 3000 RPM, and above that, it only idles. I haven't tried testing the top speed yet.'

Otherwise, it sounds quite similar.

On Wednesday, we'll check the cat litter box (or whatever is left inside).

I will post the result.

Sure, no problem! Here's the translation:

'Thank you for now!!'

News:

A friend disassembled the catalytic converter and found that it wasn't broken. To remove it, he had to fiddle with some wires, etc.

After reinstalling it, the performance was restored and the car drove normally again.
When I got home, a large oil spill had formed underneath my car in what seemed like no time. So, the next morning, I called the ADAC (German Automobile Club) to have them tow the car to the workshop. I couldn't locate the source of the heavy oil leak; everything in the engine compartment was simply covered in oil.

At VAG, the oil line to the turbo was replaced.
Now I was happy that everything was back to normal.
However, now: The engine has no power anymore.
Now I'm back to the same situation as I was over 2 weeks ago. The only difference is that I now know what isn't broken, and overall I'm two vacation days shorter and almost 300 euros poorer.
Ps. Er dreht nach dem Anlassen jetzt nicht mehr hoch. Den Doppeltemperatursensor habe ich zwischenzeitlich auch gewechselt. Without any changes.

I am thrilled.

I've also ordered the repair kit for the shut-off valve. I will install it myself sometime this week. I'll keep you updated.

Kurbelgehäuseentlüftung frei? Wenn nicht -könnte- es sein, dass nach Abstellen des Motor Öl in den Brennraum gelangt (das aus der Ringzone) und dieses verbrennt beim Start. DahHe's revving it up.

Disconnect the hose and check if it's releasing air with the engine running. Alternatively, carefully open the oil filler cap while the engine is running and see if there's an excessive amount of pressure escaping (be careful, consider wearing eye protection!).

Temperature sensor replacement unsuccessful.

Installing the repair kit for the shut-off valve (a plastic pin with a magnetic metal piece and a spring, costing around 10 euros) restored the performance, even though VW claimed that there was no such fault.

Thank you for maintaining the error database with helpful tips, and to everyone who gave me advice here.

Sure, here is the translation of the text from German to English:

'VG' translates to 'Very Good' in English.
Michael.