Boost Pressure Too High - Need Help!

Audi Avant TDI, 96 kW, manufactured in April 2003, and chipped (tuned).

It works perfectly from the start! But recently, when accelerating hard or driving at higher speeds (from 4th or 5th gear onwards), and only then, it switches to 'limp mode.'

Turning the ignition off and on again: everything's fine! (until you accelerate to full speed).

Error: Turbocharger pressure exceeded limit.
The solenoid valve has already been replaced, but there's been no improvement!

Audi sucht schon seit 7 Tagen diesen Fehler. Nächster Termin erst am 6.11. That's annoying.

'This weekend, I drove about 400 km on the highway. It happened once on the way there and once on the way back. Turning off the ignition and then turning it back on fixed the problem. Before, it would happen every time I drove at full throttle. Now, it only happens occasionally.'

Chip has been inside for 6 months and has never caused any problems (since 8,000 km).

The Audi needs to drive approximately 100 kilometers on the highway for the error to reappear.

Who can help?

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.

Hi,

The search function is your friend.

"Enter 'boost pressure exceeds limit', check the box 'search for all words', and you'll be overwhelmed with potential solutions!"

/viewtopic.php?t=3285&highlight=ladedruck+regelgrenze+%FCberschritten

That should be enough information to get you started with troubleshooting.

Hello,

It sounds suspiciously like a stuck VTG (vehicle traction generator).
Also, take a look at 'boost pressure, exceeded limit' in the search function.

Regards,

Sepp.

The boost pressure control might be at the end of its operating range... (assuming the mechanical components are functioning correctly)... which can be checked using VAG-COM and a test drive. This issue only occurs under full load, i.e., when there are high air volumes flowing through the turbocharger.
Let's refine the chip...
Stay cheerful.
OlBe.

First of all, thank you for your contributions.

Of course, I've searched all the forums and read and carefully studied all the posts.

'I went to the mechanic today, and he said it could be the mass airflow sensor, the EGR valve, or the pressure sensor.'

The vehicle has been working perfectly up until now.

I haven't found a solution anywhere so far.

Ideas?


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.

olbetec wrote:

The boost pressure control might also be at the end of its operating range... (assuming the mechanism is functioning freely). This also only occurs under full load, meaning high volumetric flow rates through the turbo...

Hi,

I would like to agree with that assumption.

Based on my experience, there can sometimes be minor issues with the turbocharger calibration when doing turbo modifications, but these can often be resolved by adjusting the variable turbine geometry (VTG) rod.

Given that the input energy for the charger is significantly increased in both cases, I believe that, even in the case of Leminem, attempting to rotate the VTG rod would be worth a try.

Hello,

That would also explain why he's only encountering the regulation problem now.
Lower intake air temperature = higher mass airflow.

@leminem

Could it be that the entire process only worked so far under significantly warmer outdoor temperatures?

Regards,

Sepp.

Okay, Sepp.

Now that it has gotten colder (between 1 and 6 degrees Celsius), the problem has also appeared.


Ideas?


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.

Hi,

It doesn't necessarily have to be the VTG.
I could also explain it that way.

You wrote that your car was "chipped."

There are, among other things, two characteristic maps for boost pressure. One is the target value that should or must be reached, and the other is the characteristic map that defines the boost pressure value for the emergency mode. In other words, if this characteristic map has not been "extended," it will always switch to emergency mode when you drive at full throttle.

Normally, in everyday operation, you always need some margin of error, both above and below. If you reduce this margin too much, and the boost pressure deviates from the target value by, for example, 3 seconds, the system will enter a failsafe mode.

So, if it's possible, I would like to talk to the chip tuner about it.

If you make the VTG vane longer, that should also work, because the turbo will then generally receive less or slower exhaust gases to the turbine, which will result in...
no longer quite reaching the peak pressure.

Greetings.
Thomas.

But it ran perfectly for months, even when running at full throttle!

Lower intake air temperature = higher mass airflow.
I think that's the approach.

I'll ask the tuner about it anyway.

I would appreciate more input.


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,

Please measure the duty cycle of the magnetic valve used for boost pressure regulation, just before the emergency mode is activated.
If the adjustment limit is reached but the mechanism otherwise functions smoothly, I would adjust the adjustment rod on the turbocharger by one full rotation.
It's likely simpler and more effective than modifying the chip, and in this case, the performance would also be preserved.

Best regards, Rainer.

Hello,

To better understand the principle of adjusting the control rod (extending it), I'll elaborate a bit. Please correct me if I'm wrong.
The throttle body is adjusted using a vacuum system.
The default position of the can (at zero pressure) is with the VTG (Variable Torque Gear) fully open, meaning the adjustment lever with the control rod is held against a mechanical stop by a spring force, and this stop cannot be adjusted.
In the system, the VTG (Variable Turbine Geometry) is adjusted using vacuum applied via the control valve, and this adjustment is generally performed in the direction of closure.
In the lower RPM range, i.e., at low flow rates, the variable turbine geometry (VTG) is more closed to generate the corresponding boost pressure, while in the upper RPM range, at full load (or nearly full load), it is almost fully open.
In the standard configuration (not tuned), there is still the possibility to reduce or regulate the boost pressure at the nominal power point (engine speed with maximum power) by further opening the variable turbine geometry (VTG).
However, when the system is running, especially with the standard turbocharger and when the upper RPM range receives significantly more fuel injection, the turbine's capacity is fully utilized even with the VTG (Variable Turbine Geometry) fully open, meaning that further control via the timing valve is no longer possible.
If the control rod is extended, it means that the maximum travel limit in operation is reached more quickly (safely) by increasing the pre-tension of the spring in the control housing. However, fundamentally, this cannot increase the maximum throughput of the turbine.

thoughtful greetings

Sepp.

Hello Sepp,

You've correctly understood the connections!

Quote:

If the control rod is extended, it means that by increasing the pre-tension of the spring in the control housing, the maximum travel limit is reached more quickly (safely) during operation. However, fundamentally: this cannot increase the maximum throughput of the turbine.

This is true, depending on how your boost control system is set up.
On my VNT15 charger, and on two others, there are threads for mechanical limit switches for the VTG adjustment, but these are not fitted with the corresponding adjustment screws.
The minimum and maximum travel limits are determined by the resting position of the adjusting rod in the vacuum chamber, as well as the position when the vacuum is at its maximum (rod fully retracted into the chamber).
Therefore, in this case, adjusting the length of the actuator rod directly changes the minimum and maximum settings. This, in turn, affects the duty cycle of the solenoid valve used for boost pressure regulation, due to a change in the spring preload within the housing.

If the strokes were additionally limited by adjustment screws on the loader, these would also need to be adjusted, if they can even be reached (since the total adjustment range is determined by the lift of the vacuum sensor).

However, I haven't seen a single loader where the adjustment screws on the VTG (Variable Geometry Turbine) were actually installed; instead, I've only seen ones where the adjustment range and the minimum/maximum positions were determined by the length of the adjustment rod and the stroke of the vacuum sensor. Of course, that doesn't necessarily mean that it always has to be that way.

Best regards, Rainer.

Hello Reiner,

If you adjust the attack points in the control unit, you are essentially shifting the adjustment range towards increased flow. However, this is not without risk, as you don't know how close the impeller blades are to the turbine wheel. The GT-VTG series from Garrett and the corresponding counterparts from KKK for VW/Audi PD-TDI diesel engines, which I have examined more closely (03825319N or H), all have an adjustable minimum stop and a fixed maximum stop inside the housing. I believe that no further adjustment is possible here.

Regards,

Sepp.

Hello Sepp,

Quote:

If the shims are inserted into the control box, you are essentially shifting the adjustment range towards increased flow rate.

However, this is not without risk, as you don't know how close the blades are to the turbine wheel.
"So far, I've always had enough space. I believe that even without any stops on the charger, it's not possible for the adjustable vanes to come into contact with the turbine wheel, because the maximum adjustment range is definitely limited by the movement of the ring mechanism within the charger."

Quote:

...I have examined several Diesel PD-TDI injectors (specifically models 03825319N and H), and they all have an adjustable minimum stop and a fixed maximum stop inside the housing. I believe that no further adjustment is possible here.

Is the adjustment lever in the "maximum boost pressure" setting at its limit during operation, or does the stroke of the adjustment pot also limit it?

A picture of your charger would be helpful here...

Best regards, Rainer.

Rainer K. wrote:

The minimum and maximum limits are determined here by the resting position of the adjusting rod in the vacuum chamber, as well as the position at maximum vacuum (rod fully retracted into the chamber).

Hello everyone,

For my loader, it's different: the lifting range of the loader-side swivel lever is approximately 1 cm, while the lifting range of the container is approximately 1.5 cm.

This means that the cylinder could potentially exert more force than the loader allows, or that I can vary the preload within a range of 5 mm, and yet the minimum and maximum lifting capacities of the loader are still reached.

As a result, the relationship between key press duration and VTG (Vertical Travel Gauge) position is shifted (within the specified 5 mm range), while the absolute VTG adjustment range remains unchanged and is not shifted.

In my opinion, this approach makes more sense than relying solely on the adjustment of the threaded rod to determine the minimum and maximum positions of the VTG (Variable Geometry Turbine).