LMM Signal vs. Fixed Value: What Happens?

... how do you incorporate resistance?

Hello there!

The car would need to make a strong hissing sound during acceleration until the boost pressure is built up accordingly. The mass airflow sensor (MAF) map acts as a limiting factor; it reduces the fuel injection amount when the actual air flow is less than what is specified.
If we now send a signal indicating that the LMM (Ladedruckmessgerät - Mass Air Flow sensor) is at its maximum capacity, then only the fuel injection map would need to be the limiting factor.
Of course, all of this only works if the system doesn't check the mass flow rate for plausibility.

Best regards, Georg.

The LMM (mass airflow sensor) can be removed if you build a digital replacement circuit with a pressure sensor. My chip tuner has already implemented this for the BMW M3, and it works very well. He is now considering developing it for diesel engines as well. However, it would require a significant amount of development effort, and therefore only becomes cost-effective at certain production volumes. The price would then be roughly equivalent to that of a new LMM. If he actually goes ahead with this, you will never have LMM problems again.

'I once brainstormed with some fellow students about how to replace the LMM (likely referring to a Mass Air Flow sensor). For example, we considered using a laser tuned to a specific gas, like oxygen. However, the problem is that it's the mass of air that's important, not just the pressure. That's why I can't quite imagine how you would measure the mass with just a pressure sensor.'

My AFN is running without a mass airflow sensor (MAF), which effectively acts like a fixed resistor (I'm not sure if it's set to zero or infinity). However, it's not performing very well. I think the engineers probably implemented some kind of emergency mode in that situation.

Or am I wrong?

Regards,

caddy

'To be honest, I'm not entirely sure about the details, but it works perfectly on the M3. You probably need to install a pressure sensor and an intake air temperature sensor. Then, you extract the characteristic curves of the mass airflow sensor (MAF), meaning the values for all engine speeds and load conditions, plus the values displayed by the pressure sensor and the temperature sensor. The result shouldn't be quite as accurate as the original MAF, but very close, so that the engine functions 100% correctly and the emissions readings are correct. That's all I know, but as I said, it works really well on the M3.'

Okay, those values are then programmed into a small add-on device with a digital circuit, which replaces the mass flow meter.

Georg_G wrote:

... What happens if you install a fixed resistor instead of the LMM signal? The car would need to make a strong hissing sound during acceleration until the boost pressure is built up accordingly. The mass airflow sensor (MAF) map acts as a limiting factor; it reduces the fuel injection amount when the actual air flow is less than what is specified. If we now send a signal indicating that the mass airflow sensor (MAF) is at its maximum reading, then only the fuel injection map would need to be considered as a limiting factor. Everything, of course, only works if the control system does not check the mass flow rate for plausibility.

Hi Georg,

Your theory seems correct, in my opinion... with the exception of the EGR issue: when the EGR valve opens, the engine control unit expects a decrease in the mass airflow (MAF) value. If this doesn't happen, the ECU fully opens the EGR valve.
Therefore, in my opinion, disabling the EGR system is mandatory in such tests. However, it doesn't really matter anymore because operating without a mass airflow sensor (MAF) is already .

What good is that supposed to do?

The electronics of TDIs offer much more possibilities. You can achieve the effect directly by modifying the characteristic maps. Why then a separate device? Furthermore, these Alfa-N devices are not exactly easy to tune on every turbocharger. It's simpler with gasoline engines, but even there, the effect in terms of increased power is more than sufficient.


@gerog_G: What do you mean by an injection quantity map? Every TDI has at least 3 of them, each weighted differently based on various parameters.

Best regards.

The idea came about because the 6-cylinder TDI engines often have problems with the mass airflow sensor (MAF). My tuner has customers who need a new one every three months. If this issue could be resolved, it would eliminate a recurring problem. It's clear that tuning and development would be very challenging. However, if it could be made TÜV-approved (German technical inspection), then people who are frustrated with the MAF sensor problems would definitely buy it.

Hi,
From a hardware perspective, the 'LMM replacement electronics' shouldn't be particularly complex. It could include a PIC 16F877 as a controller (which has built-in flash memory and an ADC), a few operational amplifiers for signal conditioning, a serial DAC (e.g., LTC1661), and some miscellaneous components like voltage regulators, resistors, and capacitors.
Cost: under €50.
The microcontroller reads the analog values from the available sensors and uses them to index a lookup table that contains the values for the 'mass airflow sensor output' (DAC).
The problem (and this is where I believe the biggest effort lies) is with the characteristic map(s).
First, suitable sensors need to be found. In the newer TDi models, the turbocharger pressure sensor is easily accessible, making it a good option. However, in older models, it's located within the engine control unit (ECU). In that case, alternative values would need to be used, such as pedal position (but what happens when the gasoline direct injection system is active?), and engine speed (okay, this isn't an analog signal but a frequency signal), etc.
Then these values must be interpreted in such a way that a value is obtained under all operating conditions that is approximately equal to the correct mass flow rate (MFR) value.
IMO would be a nice topic for a thesis in the field of control engineering (probably not 'legal' enough for a diploma thesis).

Here's a thought process about why you might need an LMM (Lambda Measuring Module) instead of directly calculating the air mass based on boost pressure and air temperature after the turbocharger:

The boost pressure is part of a control loop. If this signal is fed back into the control loop (fuel injection quantity), it can have negative effects (oscillation, resonance, etc.).
Therefore, it is certainly sensible to take a primary signal outside of the control loop. Furthermore, the signal from the mass airflow sensor is likely relatively "fast" (the actual and displayed mass air flow values have only a short time offset), which is good for minimizing oscillations.

"There are people here who work with or study control systems professionally. Maybe someone can confirm or correct what I'm about to say."

Best regards, Georg.

Okay, as someone who drives an AAZ car, I'd like to offer my opinion on this.
My engine is fully mechanical. It simply measures the boost pressure and transmits this information to the ESP (Electronic Stability Program). This system is called LDA (Ladedruckanreicherung - Boost Pressure Enrichment). The signal that can be measured there changes abruptly because the engine doesn't draw in air constantly. Therefore, it needs to be smoothed and dampened significantly.

I see another problem: Your small electronics also need to detect the motor speed. Because, even with low pressure, you'll have a high airflow at high motor speeds.
In my opinion, you need three key factors to replace an LLM:

1. Turbo pressure (without it, things get complicated).
2. Motordrehzahl (sehr wichtig. Sure, I can help you with that. Please provide the text you would like me to translate from German to English.
3. Intake air temperature (relatively unimportant).

You definitely need the intake air temperature, not the outside temperature. The intake air temperature is directly related to the boost pressure. Depending on the airflow over the intercooler, both values will vary in relation to each other.



Another question for Georg_g:
Let's assume that the temperature is constant.
Doesn't the amount of air at a specific engine speed behave non-linearly with respect to pressure? So, if resonance can occur with pressure, shouldn't it also be possible with the amount of air?

Quote:

Another question for Georg_g: Let's assume that the temperature is constant. Does the amount of air at a specific engine speed not behave linearly with pressure? So, if resonance can occur with pressure, then shouldn't it also occur with the amount of air?

You are absolutely right about the pressure/volume relationship. I hadn't considered that the air mass is essentially a function of the boost pressure. Therefore, the mass airflow rate (MAF) is also part of the system, and resonance phenomena can occur.

Best regards, Georg.