Boost Overrun: LDA vs. VAGCOM Diagnostics

Hello everyone,

I "dry-calibrated" my electronic LDA (using a voltmeter and syringe) and was quite disappointed to see that it went up to over 1.3 bar during a test run, while I rarely see more than 2.15 (which is 1.15 relative) with VAGCOM. The regulated pressure seems to be around 1 bar, maybe a little more.

Now, the measurement path involving the pressure sensor, the control unit, the diagnostic interface, etc., isn't entirely straightforward either, but despite that, this difference remains, which surprises me greatly.

After searching the forum for over an hour, I'm now relieved (because there's often talk of overvoltages up to 1.4 sometimes), and I'm gradually starting to think in a different direction:

"The sampling rate of my device is roughly the same as VAG-COM, but it's not integrated into the logic of the control unit, which, with its single CPU, can never simultaneously perform diagnostics and control actuators with perfect precision. Furthermore, we don't know what calculations are being performed internally with the pressure data."

My impression is that the pressure readings on a VAG-COM device are generally lower than those on an LDA, which presumably displays the pressure more accurately and probably reacts more quickly.

Can anyone confirm this? Are your overboost values on the LDA also higher than what is shown via VAG-COM?

I'll check the pressure again tomorrow (unfortunately, it doesn't stay stable for long in the city...), but it seems to be correct within about 50 millibars, which is perfectly sufficient for this type of display.

Just to mention briefly... it's not about the VTG function itself, which is perfectly clear and working correctly on my car (the VAG-COM values are very similar to those from 15 months ago). It's just about observations related to the LDA (Lambda Damper).

Technically, my LDA (Laser Doppler Anemometer) is a Motorola MPX4250AP, which is connected to a rubber hose approximately 80 cm long, located near the original sensor in the pressure tube. A panel meter is connected to it via a potentiometer for calibration. Therefore, there are no issues like sluggish needle movements. I will post pictures as promised.

Best regards,

Jan.

Hello Jan,
Your display processes the analog value (pressure) almost without any filtering.
VAG-COM, on the other hand, provides the converted (discretely and processor-filtered) values.
Values. That's why the best ones often get left behind.
If at all, you would need to take the raw value from group '000', which...
but which cannot be logged using VAG-COM, although it may not be obvious.

Best regards, Rudi.

Hello,
According to the latest information from Uwe Ross, the newest version of VAG-COM allows logging of data from group '000'.
Bye.
Max.

Hi,

I need to try out the "Group Zero" method, although the regulated pressure is also helpful for fine-tuning. It's not just a snapshot like the overshoot peak.

What surprised me was that my deviation at the peak (0.2 bar) was so much larger than the set value (0.05 bar).

Certainly, this shows that the overspill can also be easily seen with a digital display .

What are your general experiences regarding the accuracy of the boost pressure readings reported by VAG-COM (or the control unit) compared to the readings displayed by a GOOD and calibrated LDA (Linear Density Sensor)?

Because the quality of my idea hinges on fine-tuning it based on the values of VAG-COM (which, in essence, isn't a bad thing, because the LDA will still fulfill its purpose).

Best regards,

Jan.