LMM Correction at AEL: A User Report

Hello,

I would like to share my experiences with the LMM (Lambda Measuring Module) on a AEL engine, installed in a Volvo 850 TDI, manufactured in 1996. Perhaps it will be helpful for others.

Problem:
The engine is making a hissing noise, even though the injectors are new, the boost pressure is correct, and the valve timing is correct.
Unfortunately, VAG-COM is not compatible with this Volvo, so I cannot access the live data.

However, it's a popometer.
"This indicates that the car, which now has a considerable 300,000 km on the odometer, didn't accelerate as quickly at low RPMs initially. The engine has a wastegate turbocharger, which requires an engine speed of approximately 1900 RPM to reach a boost pressure of 1 bar."


Suspected diagnosis:

The LMM is showing an excessively high airflow rate.
Inside the LMM (likely referring to a Mass Air Flow Meter), there is a flap that is pressed in one direction by a spring. Against the force of the spring, this flap can be opened by airflow in the intake manifold, which occurs when the turbocharger is drawing in a large amount of air.
The valve controls a mechanical voltage divider, which converts the valve opening angle into a voltage. The engine control unit (ECU) interprets this voltage as a certain amount of airflow.

It's quite reasonable to assume that the diaphragm of the mass airflow sensor will degrade over time and lose its spring force. This would cause the calibration curve to become inaccurate, and the engine control unit would be told that the airflow is higher than it actually is. Well, that's the theory.


Solution to the soot problem: Recalibrating the mass airflow sensor (MAF).

It's quite simple; you just need to loosen the mounting screw (marked with an arrow in the picture, see below) of the grinder. Then, you can rotate the grinder clockwise (which will report a lower airflow) or counterclockwise (which will report a higher airflow to the MSG), and then tighten the screw again.

I did that to rotate it approximately 10 degrees clockwise.
It worked great for me. I no longer leave a trail of black smoke behind me, but the car still has plenty of power once the turbo boost kicks in significantly.


Appendix: Image of the LMM from the AEL.

hello

Thanks for the tip. Good approach...

For more in-depth diagnostics, there's a good program called "brick-diag" - which was developed by Daniel and is also distributed on the Volvo forum. It's quite advanced for the TDI and provides a lot of data.

What personally worries me a bit is the fundamental definition of soot.

When I bought the V70 TDI 8 years ago with approximately 100,000 km, I was initially shocked (before that, I had the beautiful 20v turbo 850...). It was really noisy.

In the meantime, I had four Volvo TDIs. I also replaced or serviced almost everything that typically needs attention over 300,000 km. Because I had multiple of the same vehicles, I was able to swap some parts back and forth and directly experience the difference (like with the mass airflow sensor).

Based on my experience, I quickly came to the conclusion that the vehicle, or rather, the engine, simply produces soot – it's just part of how the engine works. I find it almost impossible to operate the engine at its rated power without producing soot.

So, in a way, I had come to terms with the soot – especially since it definitely decreased over time (I had a chip tuning done, and the injectors were serviced...).

You might be right that changing the LMM (lambda sensor) reduces engine noise. However, you can also do the opposite (DIY tuning), which might cause the sun to set behind you, but the car will also have more power.

"Oh yeah, after I bought a beautiful D5, the TDI was demoted to a second car. The D5 also has over 200,000 km, is 7 years old, and has been regularly serviced. In the 10,000 km I've driven it, I've never seen even the slightest amount of soot from that engine (as a driver, looking in the rearview mirror, you know how it is with TDIs when the soot 'hangs' behind you...)"


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

"Hello"

Hi.

I'd like to revive this thread because this is a current issue for me.

To be honest, I don't know where to start with the "10 degrees clockwise" setting – it would be great if there was a value that could be adjusted.
For example, on the CR D5 model, the manufacturer states that the output is between 45 and 60 kg/h.

Is there a similar value available for the AEL TDI? Because I don't think it's a good idea to just start tinkering with things without knowing what you're doing.

Best regards,

Hi,

Quote:

I don't think it's a good idea to start tinkering with something blindly.

That's why, as a rule, the old position is marked.
When the potentiometer arm is at 10 degrees clockwise, it's positioned further towards the "open" or "high airflow" setting; the opposite direction would be rather pointless.

Best regards, Rainer.

Thank you, but that can't be right.

Mein LMM ist 500000km alt. Oder nur 40000km, weil er ersetzt wurde? Who knows that?
Therefore, I would consider it useful to adjust the value to a baseline using a diagnostic computer, or to check it beforehand.
And that's exactly what I need.

"Thank you."

best regards, uwe

Hello Uwe,

You can calculate the "base value" from the volume of the cylinder.
It is likely to be around 480mg/hour, without considering the EGR system.

Conversion from mg/H to g/s:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Best regards, Rainer.

Hello,

You're very welcome, that's already helpful.

Okay, so we have a conversion, but that doesn't explain how the value of 480mg/H is obtained. There must be manufacturer specifications available that I'm missing, especially for the engine.

Or is that a fact regarding the 480mg/H?

Thank you!


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

"Hello"

At sea level, the density of air is approximately 1.2041 kg/m³ (0.0012 g/cm³) at 20°C, and about 0.00097 g/cm³ at 90°C.

A cylinder has a volume of approximately 2461 cm³, so dividing that by 5 gives us 492.2 cm³.

"This results in an air volume of 492.2 cm³ per hub, which corresponds to 477.4 mg/hub."
"So, that fits quite well with the estimated value of 480mg/H from my previous AHF (Automated Hemodialysis Filter), and the pump volume per cylinder is the same for both the AHF and the AEL (Automated Erythropoietin Lancing)."

Best regards, Rainer.

PERFECT, thank you!!

Best regards, Uwe.