T4, ACV zu wenig Ladedruck - Lösung gefunden!! | Posts 16+

Well, there's still the option of replacing the mass airflow sensor diode...

Hello.

This car has a problem with the O-ring where the pipe connects from the mass airflow sensor (MAF) to the turbocharger; it's defective.
You can easily tell if there's a leak by shaking the pipe and listening for air escaping. If there is, the mass airflow sensor (MAF) will be measuring incorrect values because it's also drawing in that extra air.
Then you won't be able to build up any air mass, and you also won't have any boost pressure or power.

Hello!

With great joy and a little bit of pride, I announce that I have found the error!

And specifically, the exhaust pipe was blocked. You read that right, the exhaust pipe. After a lot of pondering and studying, I noticed the somewhat strong smell of exhaust fumes, which is actually not normal for a TDI; they usually all smell kind of like a catalytic converter, or something like that! That was somehow my clue. I then removed the catalytic converter and, lo and behold, the catalytic converter tube was empty at first glance . Then I looked more closely and discovered a blockage in the first bend after the catalytic converter. After a few hammer blows, pieces started to appear...

Then I asked the owner if he had ever noticed any rattling coming from the catalytic converter... He said it had rattled for a while, but after a long highway drive, it stopped. Apparently, the catalytic converter had come loose internally and the vibrations caused it to shrink in diameter until the rest of the turbocharger was blown into the bend .
And with turbo engines, even a relatively small amount of back pressure is enough to significantly reduce the efficiency of the turbocharger, as my case here demonstrates!

The fact is... the bus is running like crazy again .

Thank you all again for the answers!!! And maybe check the exhaust if you experience mysterious performance issues.

Greetings.
Martin.

Hi, I've been experiencing the same symptoms you described for the past 4 days. However, I haven't noticed any rattling from the catalytic converter. But during the drive when I first experienced the loss of power, I heard a loud banging noise coming from inside or underneath the car, which I couldn't really identify. I assumed something had fallen over in the car because I was transporting some construction materials and my child to the hospital at the time!
Air mass "is" is at a maximum of 610, while it "should" be at 860 mg/hub.
And the boost pressure "is" should be a maximum of 1420 kPa, which corresponds to 2080 mbar.
Then it goes into emergency mode and reduces the boost pressure even further.
I've actually thought for a while that the fuel injection system is faulty, so I already ordered a new one. However, I will definitely also take a closer look at the exhaust system!
And since I'm already at it, I might as well replace all the pressure and vacuum hoses.

The picture probably says it all .

Hello,

Thanks for the feedback! It looks like soot, right? So, the underlying cause seems to be excessive soot emissions. Are the glow plugs and intercooler pipes sealed properly? Does the EGR valve close correctly when accelerating fully?

Best regards, Rainer.

I think the problem probably lies with the previous owner...
"Driving 10 kilometers in city traffic every day for 15 years!"

Sure, here's the translation:

"It might produce some smoke, but it's a diesel engine after all!"
"The AGR system works! But the intake manifold is quite dirty from the AGR... I'm going to verschandeln it."

Best regards,

Hello!

I have the same car.

Okay, so the original problem was the LMM (likely referring to a mass airflow meter), which was also causing insufficient power and inadequate air intake per stroke.
It's been quite a few years already.
I mostly drive short distances as well.

A few weeks ago, I was at the TÜV (German technical inspection agency).
I had previously driven the car for about 20 kilometers on the highway just before that, with the exhaust system running at full throttle.
The performance is quite good, I must say.

I was present during the emissions test.
Well, mine didn't rust at all.
The examiner also said the results were excellent.