LT35: Intermittent Acceleration Issues

Hi there.
A good colleague drives an LT35 from the year 2001.
The engine is a 2.8L CR TDI with an output of 116 kW, and its engine code is AUH.
At the beginning of the year, a problem arose that...
during acceleration (below 3000 rpm), the forward thrust.
rhythmically collapses (the image shows the air mass during a).
(Regarding the acceleration process). Everything is fine from 3000 rpm onwards.
This behavior has already occurred once before, a few years ago.
It turned on and the issue was resolved by replacing the mass airflow sensor.
The initial approach was to use the same method.
Brought... nothing .
A logging run revealed that the air mass value fluctuated intermittently.
It repeatedly drops to 700mg.
He has now tested five additional LLMs.
1 x Bosch (new).
3 x Pierburg (new).
1 x Bosch (old; removed from my Octavia due to insufficient power).
Mit allen neuen LMMs tritt das Phänomen auf. Only the old...
Bosch beschleunigt sauber (aber nicht schnell ) hoch. For that.
It lacks performance.
The error memory showed the following code: "16485 - Mass airflow sensor (G70) - Implausible signal."
The colleague is checking to see if the same error occurs with the older Bosch device.
Unfortunately, it has not yet been checked.
"In my opinion, an electrical fault is unlikely because the parallel measurement..."
The signal voltage at the mass airflow sensor (MAF) shows no abnormalities, and the old MAF sensor...
is working.
No leaks in the system could be found .
The 700mg value used at the time of the error is a replacement value for plausibility errors.
Der Messbereich des LMM über Diagnose endet bei 1500mg. The actual...
The measurement range extends further (even though it is not used in the software).
The upper limit for the plausibility of LMM values is 2000mg.
One possible explanation for the entire behavior is that all the new...
LLMs (and also the one that was "deactivated" earlier this year) are too expensive.
Air masses are providing data, which is why the plausibility error is being flagged.
MSTG switches to a replacement value of 700mg (the turbidity limit then reduces the...).
Flow rate, mass flow rate, voltage are back within the valid range; acceleration is occurring.
and so on (and continues like this).
Just - why should all functioning mass airflow sensors provide excessively high readings?

Maybe someone here has an idea what's going on.

Best regards,
Micha

What else can you do besides installing a proper mass airflow sensor (with a target value above 1300 mg/H) and checking the cables and connectors for power supply and wiring interruptions?
What causes the LD? I've already seen defective LLKs on 130PS engines. Input LLK, crimp burst, and due to the hot LL, even the air guide melted .

Hello,

"It could be a leak in the charge air cooler system, which would also explain why the error is more pronounced at low RPMs."

Best regards, Rainer.

LD is slightly below the target value (maximum 300 hPa). Whether this is "normal" for LTs is a good question.
The new LLMs all provide sufficient air mass (more often than not, an excess amount).
I usually associate leaks in the EGR system or the charge air path with...
Leistungsmangel. Über 3000 rpm ist die Welt aber (auch Leistungsmäßig) ok. DeThe car.
It then quickly accelerates to 160 km/h (at which point the speed limiter kicks in).
Only the mass airflow sensor (MAF) from my Octavia has a limit of 150.
Regarding the 3000 rpm limit, I have two ideas. Either the air mass remains within the valid range.
or the software-based signal processing in the MSTG is performed with different parameters.
so that the dips are filtered out.

I could increase the replacement value in cases of plausibility errors, but that would be more complicated.
a "workaround".

Best regards,
Micha

Hello,

The air mass is far too high; your values would easily be enough for over 210 horsepower, of course, without producing any soot.

Given that such injection quantities are highly unlikely, I am left with two fundamental causes for the problem:
- There's a leak somewhere where air is escaping, but this airflow is being measured by the mass airflow sensor (MAF).
- The wrong mass airflow sensors (MAF) were installed, and the control unit is misinterpreting the input signal.

Best regards, Rainer.

dieselschrauber wrote:

The air mass is far too high; your values would easily be enough for over 210 horsepower, of course, without any soot.

It may be soot-free, but it certainly doesn't have 210 horsepower .

Quote:

The wrong mass airflow sensors (MAF) were installed, and the control unit is misinterpreting the input signal.

It's problematic that the error initially appeared in an LMM (Large Language Model) that had been functioning correctly for a long time.

Quote:

- there is a whistling sound where air is escaping, but this airflow is measured by the mass airflow sensor (MAF)

.
Hmm... why would a leak cause the mass airflow sensor (MAF) to draw in more air than it would under normal operating conditions?
I will take another look at the track before the LMM (just to make sure).
the airflow is extremely turbulent, and the entire air mass is moving around the sensor.
squeezed through).

Best regards,
Micha

Quote:

Why would it draw more air through the mass airflow sensor (MAF) in case of a leak than with a tight intake manifold?

Because the boost pressure control system tries to maintain the target boost pressure, regardless of the cost?

Try inflating an air mattress with a hole in it until it's "full," and then tell me if the air escaped and how much air you needed to inflate it.

beautiful picture
Okay, let's check the pressure of the charge air cooler system.
The mystery remains as to why it starts working again above 3000 rpm.
Let's see where the key ratio of the VTG control system lies in case of a fault.
moved.

Best regards,
Micha

Quote:

The mystery remains as to why it works again above 3000 rpm.

Because the LMM (likely referring to a Lambda Measurement Module) doesn't know the engine speed, and the output voltage always increases with increasing engine speed anyway?

Arbitrary values, just an example:
- 2000 rpm, output voltage 3.0V, actual output 1000 mg/H.
- 4000 rpm, output voltage 4.0V, actual oxygen production: 1000 mg/hour.

Now we are creating a hole in the charge air cooler through which 200mg per unit of time will escape. This corresponds to a fictional voltage change of 0.5V at the mass airflow sensor (MAF). With the same pressure in the charge air system, the same amount of air will always escape through the hole. The engine speed is irrelevant to the hole; it mainly depends on the pressure and the size of the hole.

With "Loch," we get:
- 2000 rpm, output voltage 3.5V.
- 4000 rpm, output voltage 4.5V.

At 2000 rpm, the difference is now 16.7%, but at 4000 rpm, it's only 11.1% voltage difference.

The "dip" becomes less noticeable with increasing engine speeds due to the error detection system. This is because, while a constant amount of air leaks at any given time (x), the total amount of air being drawn into the engine increases significantly with higher engine speeds.
That means that if the leak is wasting 200 mg/hour of air at 2000 rpm, then at 4000 rpm, for example, only 133 mg/hour of "excess" air would be measured.

Best regards, Rainer.

Quote:

...per unit of time

Thank you, Rainer!
Forest, tree, scales, hair...
The limit is 2000mg per injection, and volume, of course, is not a unit of time.
The sensor characteristics that I had in mind all along are time-dependent .
Let's see where we can find the leak.

Best regards,
Micha