Low RPM Performance Issues: Troubleshooting Guide

Hello,
nachdem ich bei meinem A6 mit AKN Motor nun einen neuen Turbo (Austauschturbolader) eingebaut habe, hat das Ansprechverhalten des Motors bei niedrigen Drehzahlen abgenommen! Ich habe natürlich zuvor hier im Forum gesucht und bin dabei auf die Einstellung der VTG Verstellung gestoßen. Eine Meßfahrt hat ergeben, daß das Tastverhältnis (Gruppe 11) bei max. 74% liegt. Die Eckdaten wie Vollast im dritten Gang usw. wurden natürlich eingehalten! LMM u'Sure, they're fine!'

Is my assumption correct that I can adjust the rod until a touch ratio of up to 95% is achieved?

Thank you for your responses.
Best regards,
Achim

avoso wrote:

Is my assumption correct that I can adjust the rod in such a way that a duty cycle of up to 95% is achieved?

Hi Achim,

Basically, yes, but 95% means that the Engine Control Unit (ECU) is trying very hard to reduce the boost pressure.
If even the slightest change occurs that leads to increased boost pressure (due to temperature, a long drive, etc.), the pressure will ultimately become too high.

I would shorten the VTG rod in increments of half rotations until the old steam returns – and not a millimeter further .

Hello Ulf,

As often happens - thank you very much for your quick response!

Do you spontaneously think of any other possible causes for the underperformance, or can we say that the currently observed maximum of 74% is generally too low?
Best regards, Achim.

avoso wrote:

Do you spontaneously think of any other possible causes for the underperformance, or can we say that the currently maximum of 74% is generally too low?

Hi Achim,

I spontaneously refer to the technical article on troubleshooting with VAGCOM .

"74% doesn't seem necessarily low to me, unless the value approaches 0% within the specified speed range."

I just found a measurement log with the values from the old turbocharger. The duty cycle is significantly higher overall, reaching up to 90%!
I'll try something out tomorrow and let you know the results.

Best regards, Achim.

Hi,

Don't forget that the values you measured are dependent on the weather conditions.
I didn't pay attention to the air pressure, but at low temperatures, it is definitely much easier to achieve the target boost pressure.
That means, if you now set the keyboard ratio to 95%, it's possible that your car might go into limp mode at -10°C and full throttle with high RPMs.

Best regards, Rainer.

Hello again,
Today I did some experimenting and came to the following conclusion.
In my opinion, the VTG (Variable Turbine Geometry) adjustment should not be based on the duty cycle, but rather by observing the overshoot! The difference with just one revolution is enormous!! After my initial setting, the boost pressure peaks were at 2500 mbar! A slight correction of only one revolution limits the overshoot to a maximum of 2300 mbar. In this process, the duty cycle hardly changed at all.

Thank you again for your help!
Best regards, Achim.

Hello everyone,
Isn't it the case that it's in measuring block 11?
The higher the boost pressure, the lower the duty cycle.
Okay, ich bin bereit. Bitte gib mir den deutschen Text, den du übersetzt haben möchtest.
/min mbar mbar %
2552 2030 2275 32
858 1132 1000 76.1
This is an excerpt from my test drive data, also using the A6.

Sure, here is the translation of the text from German to English:

'Hello.'

Richard.

Quote:

isn't it the case that, in block 11? The higher the boost pressure, the lower the duty cycle is

.

Hello, no, it's not that simple. It involves a regulation, and the pulse width only indicates what vacuum pressure is currently applied to the valve body of the charger.
If all the boundary conditions were the same, and you only increase the target boost pressure, then the duty cycle will decrease, which is correct.

Best regards, Rainer.

Hello Rainer,

and if the control unit detects that the boost pressure is too high,
He says to the control valve that it should reduce the vacuum at the sensor, and then the duty cycle will be relatively small, right?

Regards,

Richard.

Okay.

Okay, almost right. In my specific case (AHF - likely referring to a particular type of equipment), a high duty cycle indicates low vacuum pressure at the control valve.