Passat AFN: Strange Problem?

Hello,

I'm currently having a problem with a Passat from 1997, with an AFN TDI engine. The issue is as follows:
When the vehicle is cold and you start it, there are approximately 50 horsepower available. That's all! Once you've driven a few kilometers, that's it, and the car has its full power. So, the problem only occurs during a cold start.
"The error memory is always empty. The owner has already invested a considerable amount of money in VAG parts, without finding the cause of the problem. (Turbocharger, mass airflow sensor, boost valve, etc.) I have no idea why these parts were replaced! Apparently, they were supposedly broken?"

I've heard that a battery that isn't working properly can also be the cause? Could you please help me understand this a little better? Thank you.

luiggi wrote:

Passat, year of manufacture 1997, with AFN TDI engine. When the vehicle is cold, and you start driving, there are approximately 50 horsepower available. That's it! As soon as you've driven a few kilometers, the problem disappears, and the car has full power! So, the problem only occurs during cold starts!

"Spuck" is good

If you can't run a diagnostic tool (initially, log MWB 8 and 11 simultaneously), it would be helpful for troubleshooting to know how the power returns: does it happen abruptly, from one second to the next, or gradually?
To achieve this, you have to sometimes drive the car with full throttle from a cold start until it behaves normally: currently, the car apparently has an automatic cold-start protection system .

Hi,

The vehicle needs to be driven for about 5km after a cold start. After that, the power output increases to approximately 80% suddenly. The remaining 20% sometimes work after restarting the car.

"I tried replacing the battery yesterday, and surprisingly, everything seems to be working now. I have no idea why. I'm very curious about the reason myself. I'll keep monitoring it until Friday, and then I'll be able to give a definitive answer."

Question: What can you say about this? Could a battery that is no longer functioning properly have such a significant impact on the motor electronics?

luiggi wrote:

Can faulty battery affect the engine electronics to such an extent? Best regards

If the alternator, despite a high charging current from an old battery, still provides the full on-board voltage of 14.4 V: In my opinion, no.

However, by performing this action, you might have inadvertently eliminated some resistance points between the alternator (LiMa) and the battery, which could be causing voltage spikes in the vehicle's electrical system. I'm not sure if these spikes could affect the electronics in the way you're experiencing.

Hi,

Unfortunately, I'm still not making any progress. Replacing the battery only helped for one day (perhaps because of disconnecting the battery). That's a shame. But maybe it's also too illogical to expect a permanent fix that way?

I've noticed that when the car is parked in the sun and you start it when it's relatively cool, it runs without any problems. However, if it's very early in the morning or there's cold, rainy weather, it seems to have issues.

Who has advice on this problem? Thank you.

Hi,

Ulf has already written what you need to do...

Quote:

If you cannot run a diagnostic tool (for now: log MWB 8 and 11 simultaneously)

Or, just replace everything blindly until you randomly find the error...

I'm guessing it's a temperature sensor, but that's just a hunch...

Best regards,
Thomas.

Hello,

I wanted to let you know the solution to the problem mentioned, according to VAG.

The vehicle was taken back to the Volkswagen Group (VAG) service center. After a one-day search, it was again determined that the turbocharger is defective.

Conclusion: The old turbo (with only 5,000 km on it) must have been so clogged that the variable geometry turbo (VGT) was no longer working properly. Now, a new turbo has been installed (under warranty), and so far, it's working fine.

My question is: Is it possible that the new turbocharger, after only a few thousand kilometers, was so damaged that the variable geometry turbo (VGT) adjustment no longer worked? What do you think? Best regards.

luiggi wrote:

My question is: Is it possible that the new turbo, after only a few thousand kilometers, was so damaged that the VTG adjustment no longer worked?

Yes, that could be the case. However, that would only be true if other serious issues are also present. For example, problems with the electrostatic discharge system (ESDs) or the automatic gear recognition (AGR) system. Does your engine produce a lot of smoke?

However, excessive tuning that results in excessively high exhaust temperatures could also lead to this.

Nevertheless, I consider the diagnosis unlikely, but not entirely impossible.

Regards,
Guste.