A5 2.7 TDI - Poor performance/acceleration, possible causes: MAF sensor/EGR valve?

Hello everyone,

I bought an Audi A5 2.7 TDI with 190 horsepower (engine code CGKA), manufactured in May 2011, two weeks ago. It has 105,000 kilometers on the odometer.
From the beginning, I was bothered by the poor acceleration below 2500 RPM; that's when the turbo really starts to kick in.

The fuel consumption is between 8 and 9 liters per 100 kilometers under normal driving conditions.

I then tried to use VCDS to check the usual suspects.

Error memory is empty.
Boost pressure only reaches the target value from approximately 2500 RPM onwards.
Air mass = TARGET load 1200mg: ACTUAL, calibrated MW311 under load approximately 900-1000mg.
A new mass airflow meter (from Pierburg) didn't achieve the desired results!

Unfortunately, my control unit does not support OBD (On-Board Diagnostics), so I have to work with the available measured values.

With a bit of luck, these are also the correct measurements...

- AGR valve is verschandeln and functioning correctly!
- Air filter clean!
- U-shaped hoses and charge pressure hoses: no abnormalities detected.


During the second logging run, I included the EGR valve data and observed that it was constantly open even under full load.

Assuming a correct measurement!

Can someone please confirm this for me?
Or maybe not .



The log file is attached as a CSV file.



Thank you very much and best regards,

Maik.

If you prepare the CSV data yourself and focus on formatting rather than creating charts, I might take a look.

christians wrote:

Wenn Du die CSV selber aufbereitest, keine Diagramme, Formatierung reicht schon, schaue ich vielleicht auch mal rein.

Was für eine Formatierung?

Please upload the .CSV file raw.

The attached .CSV file contained duplicate entries, unfortunately without much meaningful information.

text
Please create a data log that includes only the target boost pressure, actual boost pressure, and engine speed. Ideally, use "Turbo" mode, meaning as many data points per second as possible. If new data points are only available every x seconds, how can one assess a slow or fast boost build-up?

Is there any artist currently working on engine control unit software?

Best regards, Rainer.

I prefer to view it using Excel.

Hi,

What does the VTG (variable turbine geometry) do when idling? Does the membrane housing have a vacuum?

Russian troubleshooting: Try directly connecting the membrane pump to full pressure and then take it for a test drive (with a slightly heavier foot). You should then see if any boost pressure is building up prematurely, which would help you identify the problem (likely the N75 valve).

He's not going to have two-stage charging after all? If so, the problem is likely a stuck or open bypass valve between the high-pressure (HD) and low-pressure (ND) turbine stages.

Hello,

@Rainer
The log was actually already in turbo mode; I had only stopped it once and then restarted it.
I'll create another log tomorrow!

@vwSchrauber
The VTG (Variable Turbine Geometry) and AGR (Exhaust Gas Recirculation) systems are electronically controlled in this engine.
At idle, both are at 0, and the actuator diagnosis also worked perfectly.
There is still an N18 valve installed for the EGR system that controls a Y-shaped connector.
A kind of pre-flap for the EGR cooler, located before the actual EGR valve (which is electrically controlled).

Which values or blocks under the "measured values" section are still meaningful?
The problem is that I have very few "setpoint vs. actual" comparisons among the measured values, or I'm not sure which ones go together.
Why is the actual mass airflow rate (LMM) so much lower than the target value, or is the 311 module only responsible for the EGR rate?

@christians
I am viewing the CSV file using Ron's editor.


Thank you and best regards,
Maik.

Hello,

For the CSV files, everyone already has...
https://shop.dieselschrauber.de/kdatascope---vcds-gs-911-logdateien-analysieren-p-52.php
on the hard drive. See the Windows start menu. Any conversions that make support work more difficult and are also useless are good for nothing except for corrupting the files.

Best regards, Rainer.

Hello,

I've created new logs with the turbo mode enabled, and the times are now slightly better...
@Rainer
Unfortunately, I can't say whether anyone has accessed the control unit.
Best regards,
Maik.

Hello.

Here are two more logs, one with a smoke limiter.
I think it's very clear that the actual performance is significantly lagging behind the target, and that full pressure isn't achieved until 2500 RPM.
That's exactly how it feels to drive.
What and how can I log to narrow down the error?

Thank you and best regards,
Maik.

Hello,

A log of torque limitation based on exhaust smoke or turbidity (Nm) is useless without information on accelerator pedal demand (Nm) and torque limitation via the transmission (Nm).

Have you checked if there's a leak in the intercooler piping, or on the exhaust side between the exhaust manifold and the turbine inlet (is the temperature sensor loose?)?

Please check this. Leaks on the pressure side are easy to identify due to oil leakage.

Best regards, Rainer.

dieselschrauber wrote:

Please check this. Leaks on the boost pressure side can be easily identified by oil leakage.

Not always, I speak from experience.

If you can't identify the problem with the naked eye, it's best to pressurize the charge air duct as much as possible.

Hello everyone,

I've figured out the issue with the delayed turbocharger boost.
First, the turbocharger was replaced by Audi due to a leak in the variable turbine geometry (VTG) lever (70% covered under warranty, the remainder under goodwill).
Unfortunately, the action brought about hardly any improvement.
A guided diagnosis was also performed, but of course, no abnormalities were found.
Aber ein neuer Differenzdrucksensor wurde mir nahegelegt, da es oft Probleme damit geben würde.

I then removed and cleaned the entire EGR unit myself.
Since that modification, I now have boost pressure starting around 1500 RPM, so it was a success.
However, there hasn't been much of a change in the amount of air mass, and the acceleration feels noticeably better under partial load compared to full load.

A few days later, I removed and meticulously cleaned the DPF (Diesel Particulate Filter), EGR unit, intake manifold, including the throttle flaps.
After the installation and subsequent test drive, he suddenly adjusted the air mass at full load to a consistent range of 1100-1200 mg, and the car performed much better than expected.

Knapp zwei Wochen danach dann die Ernüchterung, SOLL Luftmasse unter Volllast wieder fest 1200mg, der IST-Wert dümpelt mit ca. 1050-1100mg hinterher und die Leistung = futsch.

Continuing the investigation with VCDS:

Suspect #1 = Oxygen sensor?
Lambda sensor electronics: Bit 0 = 11001000 .

Label file.
xxxxxxx1 - Full load control on/off
xxxxxx1x - Full load.
xxxxx1xx - Regelabweichung negativ,d.h. Mixture is too fatty.
xxxx1xxx - System error.
xxx1xxxx - Oxygen sensor signal invalid or no correction achieved through lambda probe adaptation.
xx1xxxxx - Motor in starting condition.
x1xxxxxx - Instantaneous limit or quantity limit is active.
1xxxxxxx - Regeneration of exhaust aftertreatment system

Verdächtiger Nr.2 = Abgastemperatursensor 1 vor Turbolader (zum Schutz des Turbolader)!
"However, this sensor doesn't actually exist on this motor. Nevertheless, the control unit displays an unchanged value of 842 degrees for it."
Oder bekommt er den Wert zufällig von der Lambda-Sonde?

Suspect #3 = Boost pressure sensor?
Verdächtiger Nr.4 = Steuergerät?

The following can be excluded:
Differential pressure sensor (offset 0 mbar)!
DPF (Idle: 2-4 mbar, Full load: maximum back pressure of 150 mbar)!
AGR (engaged, clean, tight, smooth operation)!
Intake manifold (clean, leak-free)!
Intake manifold flaps (clean, nothing broken, functioning correctly)!
Throttle valve (clean, shifts properly, and doesn't stick)!
AGR temperature sensor (working as expected)!
Exhaust temperature sensor before and after the DPF (both within specifications)!
Charge air cooler (blocked)!
Turbocharger (new)!

Can someone please help me?

Best regards,
Maik

Quote:

The IST value is hovering around approximately 1050-1100 mg

.
"That should be enough power. Could you log the boost pressure build-up, and then do a full throttle run up to 4000 rpm?"
- Speed (or RPM)
- Injection amount
- Quantity restrictions.

and
- Speed (or RPM)
- Quantity restrictions.
- Air mass temperature (at its peak value)
- Target boost pressure vs. actual boost pressure.

Please remember to group the Turbo button and related measurements in VCDS.

Best regards, Rainer.
PS: It might also be worth comparing the actual and target fuel rail pressure under full load to ensure the engine is receiving enough fuel (e.g., a clogged diesel filter). I'm not sure if this CR engine logs an error code in case of fuel starvation, and if so, when it does.

Hello,

I hope you can make something of it.
I haven't found any quantity limits, or is "Rauch" the limit?
All values obtained at full load.

Fuel pressure is within normal limits.

I can't find any download link for VCDS in my customer account.

Best regards,
Maik.

Quote:

Eine Mengenbegrenzung habe ich nicht gefunden oder ist das die Begrenzung Rauch!?

Yes, among other things. It's a shame that without quantity limits, the logs are useless...

Because the lowest quantity limit applies in each case.

Quote:

In meinem Kundenkonto finde ich gar keinen Link zum Download von VCDS!?

Then you have tomatoes on your eyes or accidentally created a new (empty) customer account. The customer account used for the order always applies; the email address is used for identification.

Did you click the "Turbo" button when logging, or did you perhaps miss that step? The times appearing in the log seem too slow for turbo mode.

Best regards, Rainer.

Hi Rainer,

Perhaps I can find the quantity limit under a different term in the extended measurement data?
Yes, Turbo mode was enabled.
The gears seem to be engaging from the first gear, which is probably a bit too fast.
I'm going to start recording new data from the third gear onwards.
Yesterday, the quantity/moment limit was again set to "10010000", but otherwise there were no changes.