Boost pressure exceeded limit. Need help!

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

It's working great from the start! Then, recently, when driving at full throttle or a higher speed, starting in 4th or 5th gear, it switches to 'limp home' mode.

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

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

Audi has been searching for this error for 7 days. The next appointment is not until November 6th. 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, only sporadically.

Chip has been installed 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's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to '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 reaching the end of its operating range... (with a free-running mechanism)... check it with VAG-COM and a test drive. It only kicks in under full load, meaning at high volumetric flow rates through the turbo.
Let's get the chip re-tuned...
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.

Today I was at the mechanic, and he said it's likely the mass airflow sensor (MAF), 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's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

olbetec wrote:

The boost pressure control might also be at the end of its operating range... (with a free-running mechanism). It only kicks in under full load, meaning high volumetric flow rates through the turbo...

Hi,

I would like to agree with that assumption.

Based on my experience, even with turbocharger tuning, there can sometimes be minor issues with the turbocharger's boost control, which can often be resolved by adjusting the variable turbine geometry (VTG) rod.

Given that the antriebsenergie (drive power) for the charger is significantly increased in both cases, I believe that, even in the case of Leminem, attempting to rotate the VTG (variable transmission gear) 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 system only worked so far under significantly warmer outdoor temperatures?

Regards,

Sepp.

Okay, Sepp.

Now that it has gotten colder (1-6°C), the problem has also appeared.


Ideas?


Sure, here's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to '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 running mode. This means that if the engine's control unit hasn't been "remapped" or "tuned," it will likely go into "limp mode" or "safe mode" whenever you drive it at full throttle.

Normally, in everyday operations, you always need some leeway, both upwards and downwards. If this margin is reduced too much, and the boost pressure deviates from the target value by, for example, 3 seconds, the system will enter a fault mode.

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

If you make the VTG (Variable Turbine Geometry) rod longer, that should also work, because the turbo will then, in principle, receive less or slower exhaust gases to the turbine, and therefore...
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's the translation:

'MFG' is an abbreviation for 'Mit freundlichen Grüßen,' which translates to 'Sincerely' or 'Best regards' in English.

Hello,

Could you 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'm going to try it out a bit more. Please correct me if I'm wrong.
The carburetor is adjusted using a vacuum system.
The initial position of the can (at zero pressure) is with the VTG (Variable Temperature Gas) valve 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 through the control valve, and this adjustment is generally performed in the direction of a closed position.
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 (without tuning), there is still the possibility to adjust the boost pressure at the nominal power output point (the engine speed at which maximum power is achieved). The performance can be reduced or regulated by further opening the VTG (variable geometry turbine).
However, when the system is active, 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. This means 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 can also mean that the maximum... The turbine's throughput should not be increased.

thoughtful greetings

Sepp.

Hello Sepp,

You've correctly understood the connections!

Quote:

If the adjusting rod is extended, it means that by increasing the pre-tension of the spring in the control unit, the maximum stop is reached faster (more safely) during operation. But fundamentally: this can increase the maximum. The turbine's throughput should not be increased.

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 rest 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 values. By adjusting the spring pre-tension within the housing, the duty cycle of the magnetic valve used for controlling the boost pressure can also be changed.

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

However, I haven't seen a single loader where the adjustment screws on the VTG (Variable Geometry Turbine) were actually fitted, but always 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 mean 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 higher flow. However, this is not without risk, as you don't know how close the impeller is to the vanes. 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 think there are no more adjustments possible here.

Regards,

Sepp.

Hello Sepp,

Quote:

If the jets are positioned in the throttle body, you are essentially shifting the adjustment range towards increased flow. The whole thing is not entirely without risk, because one doesn't know how close the shovels are to the turbine wheel.

So far, I've always had enough space. I believe that even without any adjustments on the charger, contact between the adjustable vanes and the turbine wheel is not possible, because the maximum adjustment range is definitely limited by the movement of the ring mechanism within the charger.

Quote:

...The diesel PD-TDI injectors, which I have examined more closely (specifically models 03825319N and H), all have an adjustable minimum stop and a fixed maximum stop inside the housing. I think there are no more shifts possible here.

Is the adjustment lever in the "maximum boost pressure" setting physically hitting its limit, or is the travel of the adjustment pot itself limiting the boost?

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

Best regards, Rainer.

Rainer K. wrote:

The minimum and maximum travel are determined here by the rest 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.

That means the cylinder could exert more force than the loader allows, or 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, within the specified 5 mm range, the relationship between key press duration and VTG (Vertical Travel Gauge) position is shifted, while the absolute VTG adjustment range remains unchanged.

In my opinion, this approach also 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).