Wave-like acceleration at medium speed, MKB BRE

Hi,

Audi A6 4F, 2.0 TDI, engine code BRE. Year: 2007.
The LMM (Hitachi) was replaced by myself because the error memory indicated a fault.

According to the knowledge available at the time, testing the old mass flow meter could only be done with an oscilloscope device that would have cost 90 euros.
The new LMM cost 55 €. It is rumored that a Hitachi component was installed in that Audi.

The error reappears after installation, but with a...
"implausible signal at the LMM" = same error message.

The appearance of the yellow engine control light does not coincide with the occurrence of the wavy acceleration.
With the wave-like acceleration that only occurs with engine oil temperatures above 50-70 degrees Celsius (not in a cold state), a loss of power is noticeable, which is what is often referred to as the "camelback" phenomenon.

After driving a bit further, the irregular running noise disappears again.
Today, I managed to run a diagnostic log using VCDS with my wife's help.
I hope that I have covered all the relevant topics.
I also included AGR "Is" and "Should" values, but I couldn't find any information on the mass air flow "Should" value. (?)

"Since I'm not a professional mechanic and I don't understand all the comments from the more experienced people here, I hope someone can tell me what information I'm missing, or whether my CSV file is useful." The file can now be used for some basic tasks.

Thank you.

Hello,

Most likely, the power limitation is due to air mass measurement (MAF), a general fuel shortage (particularly noticeable at full throttle), and a limitation triggered by what is perceived as an excessively high exhaust gas temperature.

I would first check the LMM values, then look at the quantity limits, and if those are okay, proceed with checking the fuel supply.

Best regards, Rainer.

Hi,

I understand the answer as follows:

The log values for LMM (mass airflow sensor) actual value, engine speed, throttle position (driver request), etc., should be re-created correctly using diagnostic trouble codes (DTCs) 8 and 10. The CSV file should also be cleaned to remove unnecessary data and improve readability.
The text does not mention measuring the mass flow rate using a multimeter.
Is that correct?
Ideally, when driving in "Log" mode, it would be beneficial to occasionally apply full throttle in third gear, even if it exceeds 1300 rpm.
And ideally, this should happen when the error occurs.

Is "Trübungsbegrenzung" the same thing as what's called "Rauchbegrenzung" (smoke limitation) in the MWB (German emissions standard)? (Nm)
Or is that the torque limit?
Regards,
Ronald.

Hello.

Quote:

The log values for LMM (mass airflow sensor) actual value, engine speed, throttle position (driver request), etc., should be re-created correctly using diagnostic trouble codes (DTCs) 8 and 10. The CSV file should also be cleaned to remove unnecessary data and improve readability. The text does not mention measuring the mass flow rate using a multimeter. Is that correct? Ideally, when driving in "Log" mode, it would be beneficial to occasionally apply full throttle in third gear, even if it exceeds 1300 rpm. And ideally, this should happen when the error occurs. And is "Trübungsbegrenzung" what is called "Rauchbegrenzung" in the MWB (manufacturer's instructions)? (Nm)?

Okay.

Quote:

Or is that the torque limit ?

= Limit based on torque, which should always be the lowest value among all limits when the accelerator is fully pressed.

Best regards, Rainer.

Hi,

I tried to analyze the log file LOG-001-080-010-xx_140424, but unfortunately, it wasn't possible to use full throttle during the trip, which likely made the analysis more difficult.
Despite everything, during the journey, "fortunately," the yellow engine warning light came on – and, as far as I remember, it came on repeatedly – when driving at higher speeds on the highway.
That's why I created a chart in Excel, starting from the approximate time of the highway trip, as part of my attempt to analyze the data.

It is important to note that when the light illuminated, there was no noticeable "camel jockey" effect.
And the error memory reading, which pointed to a time three days before the test drive, also showed no signs of "camel jockey" behavior. The error memory indicates, as before, an implausible signal from the mass airflow sensor.

If my data is not yet suitable for analysis, please let me know.

The PNG files of the screenshots reveal that, unfortunately, the line for the second MWB (010) was not selected.
However, everything was written correctly in the CSV file.

The images are useless. Just check if the torque limit of the transmission is the lowest limit when accelerating at full throttle.

I actually thought I had already written that.

And if the mass airflow sensor (MAF) is showing an error code, then just post it. What else?

Hi,

I hope that this file can be useful.
It is a CSV file from Ross-Tech that has been converted into an XLSX file using the Ross-Tech tool.

If I'm interpreting it correctly, the torque limit at full throttle is at least twice the lowest torque value.

Once, the value at full throttle is higher than the smoke limit.
But what does that mean?

Because it's an automatic transmission, it shifts from 3rd to 4th gear relatively quickly when you're at high RPM and accelerating at full throttle.
I assume - and I hope - that it doesn't negatively affect the test, but there's really no other way to do it.

I have now also added the error memory message from the engine control unit here.

The accelerator pedal position was almost always fully pressed (100%), which unfortunately makes the log data somewhat meaningless. In one image, titled "wave-like acceleration," the driver's desired acceleration was shown as a wave pattern.

Hi,

I have now recorded another series of trips with vehicles MWB 080 and 010, including longer periods of full acceleration.

I hope that this file is usable.

When pushing it to the limit, you could feel a slight drop in power, which should be reflected in the numbers. I unfortunately don't see where.

However, it seems that the torque limit is always below the smoke limit. As far as I understand so far, that's how it's supposed to be.

I would appreciate an interpretation of the log, if it is now useful.

Regards,
Ronald.

Hello,

You can actually see drops in both air masses, even though the accelerator pedal remains at 100%. I suspect the dips are very short but sharp, and therefore difficult to see in the measurement data (due to the low sampling rate).

I suspect there might be a problem with the wiring to the mass airflow sensor (MAF), the MAF sensor itself, or a poorly executed (faulty) chip tuning in the ECU.

The turbocharger pressure sensor and its wiring are also suspect, because the turbocharger pressure changes very quickly, along with the dropouts. In my opinion, it's perhaps too quick, as the turbine and its adjustment mechanism have a certain amount of inertia.

It's also a good idea to keep an eye on the ECU's operating voltage, just to make sure there aren't any issues with its power supply.

Is the engine control unit (ECU) software original?

Best regards, Rainer.

Hi Rainer,

Thank you for the response.

While I had a replacement engine installed 50,000 km ago, it was only to get the car running again.
The workshop, as well as myself, have no intention of doing any tuning.
I actually have no idea about that either.
I'm fine as long as the car runs.

I only replaced the mass airflow sensor (MAF) in the fall because it seemed like the simplest and cheapest solution at the time. (It was 49.90 from Hitachi, supposedly identical to the original).
I can reinstall the original part and see if a test drive makes any difference.

"It's likely that we can then rule out the MSG software as the cause of the problem, and also the suspicion pointing towards the ECU, as I have no interest in that."

Is it sufficient to check the wiring of the mass airflow sensor (MAF) by visually inspecting the cable for damage and testing the connector with a multimeter?

That's all the questions I have for now regarding the first part of your answer.
I'm sorry for the many questions, but I'm more of a driver than a mechanic.

Best regards,
Ronald.

Quote:

000257 - Air mass meter (G70) P0101 - 000 - Implausible signal. Environmental conditions: Error status: 01100000 Error priority: 2 Error frequency: 1 Lost Counter: 255 Mileage: 214,500 km Time: 0 Date: 2024.04.11 Time: 18:35:51

When dealing with such a critical issue, you shouldn't experiment with a Large Language Model (LLM) that is supposedly a good fit; instead, you should use an original part.

No, simply holding a multimeter to a cable with connectors that moves and vibrates during operation is not sufficient for testing it.

Again, you most likely have a cable/connector issue and/or an incompatible MAF sensor and/or power supply problems with the ECU, and you never reported any feedback on these issues.

It shouldn't be too difficult to thoroughly test a cable with connectors to ensure it's fully functional and to rule out any points of friction or cable breaks. If this is too much for you, the Audi authorized service center is a better place to go.

Best regards, Rainer.

Hi,

Thank you for the answer.

I have now installed a Bosch mass airflow sensor that is compatible with or contains the components of the original Bosch sensor, part number G70.

The wave-like acceleration is currently no longer noticeable.

Since I mostly drive short distances in my car, I cleaned the EGR valve and the throttle body about 8 weeks ago. Four weeks ago, I removed the intake manifold because, after removing the EGR valve, I found a significant amount of oily residue there and wanted to see how far the buildup extended.

Fortunately, there wasn't much left to verschandeln on the engine side. However, the EGR valve looked quite bad. I can provide a picture if needed.

Last week, I inspected the boost pressure hose connected to the turbo. It was oily on the outside, but thankfully almost dry on the inside. (I can provide a picture if needed).
Now that I've just installed the new LMM, I'd like to know what you think about the oil film on the old sensor. See image.
Is the oil coming from a faulty crankcase, or in which direction should I continue my investigation?

Thank you for your support.

Best regards,
Ronald.