Passat 3B MBK: AFN Engine - Black Smoke Issues

Hi,

I'm new to this forum. I'm currently trying to get a 1998 Passat 3B running again, but my options are limited. Right now, the car has a couple of issues. It's hard to start... it's probably due to a faulty coolant temperature sensor. When I disconnect it, the engine starts much better after its initial warm-up period of about 20 seconds.
The second problem is causing me much more trouble. I've managed to get the messed-up car running, and it actually drives quite well.
The only thing is, when I let off the gas and then accelerate again, it starts to emit black and blue smoke and loses power.
"It's not storing any error codes, so I suspect a mechanical issue. I'm leaning towards a problem with the VTG turbocharger, possibly with the linkage becoming too sluggish. I've already checked how the turbocharger is being actuated using a vacuum pump, and everything seems to be working correctly."

My question to you all... has anyone else experienced similar problems before?

I would appreciate any suggestions.

Sincerely,

Nils Hennig.

Hello and welcome to the forum.

It would really be helpful if you could tell me what kind of engine you have and what its mileage is .

Okay, so black smoke is already a sign of a lack of air.

Since you're seeing soot formation due to sudden load changes, you can assume that the VTG (Variable Turbine Geometry) is not responding quickly enough.

A smoothly operating VTG (variable transmission gearbox) doesn't necessarily mean it's fully functional. It can still be so dirty that it doesn't work properly.

It doesn't necessarily have to be the VTG (variable turbine geometry), it could also be a vacuum hose or the N75 (pressure sensor).

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

"MFG" is an abbreviation for "Mit freundlichen Grüßen," which means "Sincerely" or "Best regards" in English.

Hello,

Quote:

Since you have soot in the case of sudden load changes, you can assume that the VTG (voltage transformer group) is not reacting quickly enough.

Certainly not.

Because there is a "smoke limitation" map for that purpose in the engine control unit.

Blue-gray smoke = engine oil; there could be several reasons for this. Based on what you're describing, I suspect it's a worn-out bearing in the turbocharger.
If it's also emitting black smoke, that indicates a leak in the charge air system.

Quote:

It starts modestly...this is probably due to a defective coolant temperature sensor.

Okay, then just create a new one. It will take 5 minutes and cost 30 euros.

Best regards, Rainer.

Passy09 wrote:

It would really be helpful if you could tell me what kind of engine you have and what its mileage is .

The engine is an AFN... I have no idea how many kilometers it has on it. I work at an institute, and apparently, it's already a replacement engine. It's supposed to have around 50,000 kilometers, but I have no proof of that. The car itself has 171,000 kilometers on it.

Just remembered something... the problem also occurred when the vacuum hose was disconnected from the VTG valve.

I'll check with them on Monday to see if they have a loader that I can borrow to test fit.

Thank you in advance for the answers.

Best regards,
Fiedde.