Passat B5 TDI AFN, 1999, vibrates at minimum load

Hello everyone,

My car (currently with 330,000 km) had its head gasket replaced in March 2024 (at approximately 306,000 km), and the cylinder head was machined (planed) during the process.
The fuel injectors were replaced in 2022 at approximately 290,000 km with injectors from Dieselsend.
Basically, it runs smoothly, accelerates well, and starts easily both when cold and when warm.

However, it sometimes jerks when I give it very little gas, mostly when going downhill. This jerking has been happening since the cylinder head repair.
The stuttering isn't dramatic, but it's slowly becoming annoying.

The dynamic injection timing was checked in the workshop and is almost perfectly centered within the target range.
I deactivated the AGR last week, but it didn't make any difference.

I then bought an OBDeleven device. The app also shows that the fuel injection timing is correct.
However, the injection volume at 85°C is only 1-2 mg per injection (it fluctuates between these two values, trending towards 1 mg per injection).
The decimal place is always 0. The voltage in field 3 of block 1 is 1.48V.
According to the OBD11 app, all the correction values in block 13 are within the green range.
The OBD11 app didn't display any errors.

Unfortunately, the OBD11 iOS app cannot record data.
Therefore, I kept the app running during the trip and recorded it with video.
It was observed that during the jerking motion with very little throttle, the injection amount drops to 0 mg/cycle (sometimes also 1 mg/cycle), while the voltage in field 3 fluctuates between approximately 0.7V and 1.2V.

I asked my mechanic if he could mechanically adjust the fuel injection amount, but he's not comfortable doing it.
He's a veteran in this field, having run his own AFN for a long time. But I'm not taking it personally.
Okay, here are my questions for you:
* Does it make sense to mechanically set the injection amount to 3-4 mg per stroke, or is the risk too high that something might go wrong?
"If so, does anyone know of a workshop in Vienna that can reliably do this? Or is the fuel injection pump already too old or likely too dirty after 330,000 km?"
Is the shaking harmful to the engine?

Sure, here's the translation:

"Thank you in advance!"

Greetings from Vienna,
Markus.

Hello.

Quote:

Does it make sense to mechanically adjust the injection amount to 3-4 mg/stroke

?
Yes, in that case, the engine tends to idle roughly.

Adjustment with a special key for the fuel mixture control is completed in under 30 minutes. It's helpful to have an assistant who can turn off the ignition if the fuel mixture control is pushed too far in the wrong direction (causing the engine to rev up).

Okay, I understand. Please provide the German text you want me to translate into English. I will only provide the translation.
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Best regards, Rainer.

Hello Rainer,

Thank you for your reply!
When idling, it runs very smoothly, at least as far as I can tell. The jerking only occurs when I press the gas pedal very lightly.

Best regards,
Markus.

Please replace the word "Leerlauf" in my post with "low RPM under light load".

And maybe, just maybe, read some of the posts in the forum sometime...

I increased the injection amount in channel 1 to 4 mg/H.
The stuttering is gone now.
The starting behavior and acceleration are still okay.

Regards,

Markus.

meatball wrote:

I have increased the injection amount in channel 1 to 4 mg/H. The stuttering is gone now. The starting behavior and acceleration are still okay. Regards, Markus

?

So, you moved the quantity setting device, and the value in measurement block 1 changed while it was idling?

What did you do? The sentence you wrote doesn't make sense because it doesn't describe anything specific.

He probably means adaptation channel 1 of the MSG. With the older models (e.g., 1Z), it was also possible to adjust the associated EM value within certain limits, which was assigned to the MSW.
hg
Herbert.

Yes, probably!

Okay, I'm ready. Please provide the German text you want me to translate.

Sorry, dass ich mich nicht präziser ausgedrückt habe.
Yes, that's exactly what I meant.
I reduced the default value (32768) to 32645 (which should be the minimum). As a result, the displayed injection amount increased from 1.0 mg/H to 4.0 mg/H.

As mentioned in this thread /viewtopic.php?t=1590, the fuel gauge now shows a slightly higher reading.