AVB zeitweise LuMa-Mangel (Lösung: VTG schließt zu weit) | Posts 16+

Gestern noch ohne Auspuff gefahren, gleich hinter Turbo getrennt. Similar symptoms.

Today, I secured the bypass valve with a wire to prevent it from opening. There's been no change in the power loss issue. I need to remove and inspect the EGR/bypass valve housing more closely in the next few days, but I won't be doing that today, Sunday.

"It's currently clicking because too few valves are opening due to low oil pressure (meaning the hydraulic lifters aren't fully filled), but it should be making a clattering noise instead."

Could you please upload the Excel file for that chart? I'd also like to see a Luminescence/Lifetime relationship.
I'd like to add something, but I can't figure out how you did it. It took me quite a while to get the diagram right. I'm not an Excel expert.

Thank you.

Hello,

Quote:

I'm already tapping on too few opening valves, due to low oil pressure (meaning the hydraulic lifters aren't fully filled), but in that case, it should be making a clattering noise.

You wrote that if you briefly release the accelerator and then press it again, the error disappears.
If there were problems with the valves, this would depend on the oil pressure or oil supply. However, this primarily depends on the engine speed (the oil temperature doesn't change that quickly), not how far the accelerator pedal is pressed.
Releasing the accelerator slightly and then pressing it again shouldn't have much effect, as the engine speed will hardly change.

Best regards, Rainer.

chli1976 wrote:

Ulf, could you please upload the .xls file for the chart? I'd also like to add a Luminescence/Lifetime (LuMa/LD) relationship, but I can't figure out how you did it.

See attachment.

Yes, Rainer, it should be like that, but I don't know what else to try anymore.

Turbo+N75 replaced (someone else had already replaced it for me due to this problem).
Checked the intake hose for any constrictions.
Tried LMM, does it work?
Covered with metal sheet.
Smoke plume elevated.
Driven without an air filter.
Vertical turbine generator shaft checked for clamping, with a differential pressure of 180 mbar at the base setting.
Driven without a muffler.
Shut-off valve deactivated.


To trigger it, you need to lower the speed until it reaches the idle level (LL) and then accelerate.

I spoke with the driver again. He mentioned that the problem occurs more frequently when the engine is cold.

The car has 130,000 km on it. Assuming there isn't a narrowed intake manifold, that issue would also need to be present all the time.

Which control modules interact with the N75 valve? When I compare the VCDS values with the control module map, it only matches when the car is running normally.

There's also a PID (Proportional-Integral-Derivative) control system, or am I wrong? Rainer, you probably know more about this.

chli1976 wrote:

Which control fields still access the N75? When I compare the VCDS values with the control field, it only matches if the car is running normally. There's also a PID amplification, or is that incorrect?

That's already correct. They adjust the charger control based on the characteristic map as soon as regulation errors occur.
Here, they operate normally by reclosing the VTG (Variable Transmission Gear) if the desired load is not reached.

If you can rule out any (spontaneous) restrictions in the gas passages, then only incorrect mass flow meter readings remain as a possibility. These can also occur even with a functioning mass flow meter if, for example, its supply voltages are not correct .

ulf wrote:

That is correct. They correct the charger control from the engine control unit as soon as regulatory errors occur. Here, they operate normally by reclosing the VTG (Variable Transmission Gear) if the desired load is not reached. If you can rule out any (spontaneous) constrictions in the gas passages, then only incorrect mass flow rate (LMM) readings remain as a possibility. These can also occur even with a functioning LMM if, for example, its supply voltages are not correct

.

However, I've also tried increasing the ignition timing based on the torque limit values, and it doesn't work correctly there either. This is to rule out any errors related to air mass measurement.

The engine's fuel map currently only works based on RPM and fuel injection volume; therefore, there must be another map that corrects this value depending on the load (LD).

chli1976 wrote:

The engine control map only works based on RPM and fuel injection amount; therefore, there must be another map that corrects this depending on the load.

That's exactly what the PID parameters do. However, it's not a single map, but rather (the most important) 3 characteristic curves, each linked to 4 to 5 individual values.

Quote:

They can also occur even with a functioning mass airflow sensor (MAF), for example, if its supply voltages are incorrect.

How likely is it for a cable to break or for contacts to become oxidized in the early stages?
And from what point onwards will an error be flagged?

Do air masses change if you wiggle things around in the wiring harness here and there?

Autoservice wrote:

How likely would a broken cable or oxidized contacts be in the early stages?

IMO, quite possible.

Quote:

And from what point onwards is an error flagged?

As far as I know, it's when the LLM voltage goes above or below the defined acceptable range.

What surprises me is that the LuMa (likely referring to a sensor reading) practically returns to the idle value, as if a replacement value were being used after a defect is detected. However, this replacement value shouldn't fluctuate like it does in the last MWB10+11 log at 155-159 seconds and 263-265 seconds.
Unless the replacement value is calculated based on the current LD-Is: This error response can be programmed in this way, but if the calculated LuMa then decreases while the LD increases, the calculation routine would have to look quite strange .

@chli1976: Please run another MWB 10+11 log with the mass airflow sensor disconnected, so that we can hopefully see the calculated replacement values for the air mass.

Is there anything in the error memory related to the mass airflow sensor (MAF)?

There are no error codes stored in the fault memory.

I will post the log with the detached plug today or tomorrow.

Here's the log with the LMM connector disconnected.

Okay, so we're seeing a completely load-dependent and speed-independent constant value of 539 mg per cycle for the LuMa measurement.

While the fault case with a connected mass airflow sensor (MAF) may appear similar at first glance, there are subtle differences in detail.
Since there is no error entry for the LMM (Lufft Mass Flow Meter), the signal voltage is likely still within a plausible range, meaning that the LMM is recognized as active and functional, and its values are used to calculate the turbidity limit.

I would most likely suspect a temporary failure of the 12V power supply to the mass airflow sensor (MAF).
Why one can deliberately provoke this through the driving cycle is something I have no idea about .
Temporarily connect the LMM-12V to a different power source and check if the problem still persists.



Okay, please provide the German text you would like me to translate into English. I will only provide the translation.
A too low 5V supply voltage also seems plausible to me: Normally, the mass airflow sensor (MAF) voltage increases with engine speed towards 5V at maximum power (Pmax), assuming a constant boost pressure.
If the control voltage gets stuck somewhere along the way (due to a limitation imposed by the supply voltage), then with increasing speed, a decreasing amount of liquid moved per cycle is calculated, as can be seen in the penultimate log entry, starting around 2200 rpm.
As long as the supply voltage is sufficient to maintain the signal voltage above the lower error threshold, no fault will be detected.

Just to be sure: Is the software in the engine control unit original, and does it actually belong there?

To the best of my knowledge, nothing has been changed here, but I will double-check it again.

ulf wrote:

Okay, so we are seeing a completely LD- and speed-independent LuMa fixed value of 539 mg/stroke.

Yes.
"And the acceleration, including the initial setup and adjustments, works quickly and easily from the second attempt! It just doesn't work when trying to accelerate initially."
In my opinion, it can't be *just* due to an incorrect LMM value. There must be something else wrong with the VTG control system. Or is the smoke limiter still deactivated?
Unfortunately, the MWB 8 is missing. I will make sure to log it in the future.
haithamina

MWB 8/4 contained between 29 and 32 mg per dose.