VTG Issue: Troubleshooting and Solutions

Hello everyone!

My VTG (Variable Turbine Geometry) system seems to be developing a life of its own, as the behavior of the turbocharger's control has been extremely surprising lately.

The pressure levels, which are often exceeded, can reach dizzying heights of 2500-2600 millibars, which not infrequently leads to emergency run scenarios .
The pressure is enormous that the loader already achieves in the basic setting mode in group 11. Here, a pressure build-up of 1120-1150 mbar is already achieved at idle speed .
Even in a completely isolated system, the pressure is still around 1010-1020 millibars.

I suspect that the mechanical stop of the VTG adjustment has changed, which allows the VTG to close much further. This is also noticeable in traction mode, where the VTG is often heavily engaged, resulting in a strong braking effect from the motor.

There was a temporary issue with the finicky adjustment mechanism, but it has since been resolved.
Can the length of the regulating rod change during operation?

Who has a possible explanation?

Regards,
Alex.

donalexo wrote:

The pressure is enormous that the loader already achieves in basic setting mode in group 11. Here, a pressure build-up of 1120-1150 mbar is already achieved at idle speed

Hi Alex,

In this test, the LD- difference between VTG ON and OFF is crucial, not the achieved maximum pressure!

Quote:

In a completely isolated system, the pressure is still around 1010-1020 mbar.

If this is the "VTG-OFF" value, the difference would be approximately 120 mbar, which is not unusually high, but within the normal range.

Quote:

I suspect that the mechanical stop of the VTG adjustment has changed, which allows the VTG to move much further "closed." This is also noticeable in driving mode, where the VTG is often heavily engaged, resulting in a strong motor braking effect.

The only solution is to re-adjust the stop (-> see technical article). Can you see on the VTG lever whether the stop screw has become embedded there?

Quote:

Can the length of the control rod change during operation?

No, but the pressure-travel curve of the diaphragm chamber can, for example, due to a broken spring or similar. -> If the diaphragm chamber closes the VTG too much with low vacuum, your problem could also be (partially) explained by this.

donalexo wrote:

... Who has a possible explanation? ...

Air filter closed, VTG sensor stuck.

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

@Ulf:

The pressure difference of the turbocharger that I mentioned refers to an idle speed of 903 RPM, and not to the increased speed of 1400 RPM!!!


@all:

New data logging has once again confirmed that the engine is being over-pressurized to over 2500 mbar under high load and at engine speeds above 2000 RPM .
The regulation is obviously completely ineffective, as the duty cycle remains at 94% and it cannot reduce the pressure .

Certainly, the membrane diaphragm could be stuck, or the VTG (vertical travel gauge) could be catching in the closed position, but for a strange reason, I can't quite believe that:
I regularly perform a test (usually in 2nd gear) that involves a full-throttle acceleration at low RPM followed by a gear shift. When shifting up, the engine control unit (ECU) immediately reduces the turbocharger boost pressure via the clutch sensor. This regulation process, i.e., the adjustment of the variable turbine geometry (VTG), can always be clearly heard as a hissing/whistling sound.

In this situation, the pulse width is abruptly increased, and the canister clearly detaches from its position, producing a noticeable acoustic sound. Certainly, the exhaust mass flow also decreases sharply due to the reduction in electrical power during the switching process, but even so, I don't think you would immediately hear the hissing sound if the canister were stuck, would you?

I can logically rule out a leak in the vacuum system because that would typically result in a slower build-up of boost pressure and a tendency towards lower boost pressure. In my case, it's exactly the opposite.

I also find it hard to believe that the pressure transducer is defective, because hopefully it's designed to be fail-safe, meaning that in case of a defect, it would only connect to the ambient pressure and not to the vacuum, right?

I wish I had the time and opportunity right now to inspect the loader linkage from underneath (using a syringe and my hands). Unfortunately, with the current temperatures (down to -15°C yesterday) and my current workload, it's impossible.
I'm starting to get really worried that I'm going to damage the head gasket and/or the loader.

Does anyone have any other ideas?

Regards,
Alex.

Hello everyone!

Yesterday, I solved my problem. I had the opportunity to inspect my loader from underneath in a pit.
The VTG (Variable Turbine Geometry) was so severely clogged that it's almost unbelievable . Especially considering it only had 15,000 km (approximately 9,300 miles)!!! I completely disassembled and cleaned the turbocharger before installation, and after such a short period of use, the VTG was completely seized.
However, I also have a plausible explanation for how this could have happened. To make it easier to access, I removed the membrane housing from the loader. Even with moderate force applied to the lever, the possible adjustment range was only a few millimeters.
It took a lot of patience and brute force before I could finally reach the "min." setting again after countless attempts with various settings.
I then wondered how it could be that the minimum setting gradually shifts towards the maximum setting over time due to carbon deposits. The solution to this puzzle is relatively simple, at least in my case:
The adjustment arm is pressed towards the minimum position solely by the spring force. By its very nature, the spring exerts its minimum force in the vicinity of the minimum position and its maximum force in the vicinity of the maximum stop. Consequently, a relatively small amount of play in the area of the minimum stop can no longer be overcome, which leads to a gradual shift of the minimum point towards the maximum stop.
I noticed that the control rod on my loader was set relatively short, which meant that almost no pre-tension force was being applied in the minimum range.
After adjusting the mechanism, I extended the rod by two rotations, which significantly increased the preload force in the minimum range. I hope that this measure will permanently ensure that the VTG remains unobstructed.

While I now notice a slightly delayed pressure build-up in the handling, I don't find it disturbing. Rather, it should also help to reduce harmful oversteer.

Regards,
Alex.

donalexo wrote:

The VTG (Variable Turbine Geometry) was so severely clogged that it's almost unbelievable . Especially considering it only had 15,000 km (approximately 9,300 miles)!!! I completely disassembled and cleaned the turbocharger before installation, and after such a short period of use, the VTG was completely stuck.

It reminds me somewhat of my 1997 AFN, although it wasn't quite as bad in that case. The mileage from new to the first problems (sometimes no boost, VTG stuck open) was in a similar range.
For me, a larger loading dose provided a lasting solution.