LMM Contour Lines: Definition & Calculation

Hello,

I would like to use this thread to collect characteristic curves for various mass flow meters. In some cases, a different characteristic curve may be more suitable for certain applications.

Okay, I'll start with:
074 906 461 B or BX (Bosch part number 0 281 002 461/462 or 0 986 284 007).
integrated into ASZ/AVF systems.


dm/dt [kg/h]: U_A nominal [V]
10: 1,2312
15: 1.3666
30: 1.6965
60: 2.1841
120: 2.7491
250: 3.4715
370: 3.9158
480: 4.2316
640: 4.6073

Best regards, Matthias.

Hello,

The request to Bosch regarding alternative characteristic curves has resulted in a negative response .
'Does anyone know of a turbocharger that is electrically and mechanically compatible and available as a replacement part through VAG, which has a more aggressive performance curve than the one I specified?'
Or do I really have to create an amplifier circuit?

Best regards, Matthias.

Hi,

"Seriously, for 85 euros? My suggestion: either modify the software in the control unit or take it to the dealership."

Best regards, Rainer.

Hi,

I'm not sure how the customer service representative could help me. They clearly have no idea about the characteristic curves. Furthermore, it would cost me multiple times 85€ before I find an MAF sensor with a different characteristic curve. Unfortunately, I don't have the ability to make any changes in the MSG (presumably a software or system).

Best regards, Matthias.

I thought your LMM (lambda sensor) was simply broken. What's the problem in finding an LMM with such an unsuitable characteristic curve that the EGR is deactivated, while the rest functions as usual?
You're unlikely to find someone like that.

Best regards, Rainer.

Then, electronically adjust the characteristic curve. If you know the actual and target values, it's not really that difficult, unless there are supposed to be 5 inflection points.
Tell me where it should go; maybe someone will have an idea.
However, I don't think it's worth the effort to add anything to something that's already broken.

Best regards,
Christian.

Hello,

I don't want to damage my probably broken mass airflow sensor, especially since a new one will be installed soon anyway.
See /viewtopic.php?t=7254&postdays=0&postorder=asc&start=24
I posted some logs there. I'm concerned that the vehicle is running within the soot limit range up to approximately 1500 min^-1. However, my air mass at idle is too low, at 400mg/H. Perhaps the problem doesn't exist to this extent with a new mass airflow sensor (MAF). With high air masses, the MAF value seems to be correct. However, my MAF sensor seems to have deficiencies only with low air mass flows and in its response behavior.
Since I'm getting a new LMM anyway, I wanted to take the opportunity to get one with a steeper characteristic curve, in order to rule out the possibility of being below 1500 min^-1 in terms of soot reduction.
Therefore, the question is about the other LLMs. Since there are likely no answers available for this question, I will probably have to resort to using the original LLM and then potentially modify it.
Essentially, it's similar to the diode replacement: disabling the soot limit function, and the improved mass airflow sensor (MAF) value enhances the response because, when the accelerator pedal is pressed, the system injects fuel at full capacity immediately, even though the load and, consequently, the MAF value haven't yet reached their maximum.
However, by using the diode, I'm going from one extreme to another. With a mass flow meter (MFM) that has a steeper characteristic curve or has been modified, I want to find the 'sweet spot.' The goal is primarily to generate a plausible MFM signal.
With the diode, the vehicle runs smoothly for a long time without errors. Only after a certain time does the 'implausible MAF sensor signal' error appear (logically, it remains constantly around 1200 mg/H). During prolonged acceleration at high speeds (especially slightly downhill), this can lead to a severe EGR error (regulation deviation too high - which is also logical given the error ), causing the warning light in the instrument cluster to illuminate, which in itself is not a problem. There is no limp-home mode. However, this may not always reveal if another, more serious error is present.
This is also an important reason why the diode needs to be replaced by an LMM (likely mass flow meter) in the medium term, even if it is a different or modified version.

Best regards, Matthias.

Hello,

Why don't you try the simplest method /viewtopic.php?t=4258?

With a resistor connected from Sense to +5V. Next, a smaller resistor and one or two diodes in series after the +5V.

Best regards,
Christian.

Hi,

That's certainly an idea. In principle, it should be sufficient if I add a specific resistor in parallel with the sensor (i.e., from the +5V line to the signal line).

Best regards, Matthias.

@matthias
I'm actually experiencing the same issues as you and have the same problems. Could you please share some pictures of how you did it? Are the new mass airflow sensors (MAF) also simple hot-film sensors?

By the way, some observations regarding the diode:
Within the speed range up to 2000 RPM, there's significantly more potential – the full torque is actually available around 300 RPM earlier. However, above 2000 RPM, where it should normally run smoothly, it experiences a turbo lag, which results in a noticeable drop in performance.
Advantages with LMM: Starts accelerating from 2000 RPM without any hesitation, quickly reaching 4000 RPM. The engine runs smoother at idle. Why is that?
(That the more you drive a car with a diode, the faster it will enter limp mode in push mode or light partial load mode due to an 'implausible mass airflow sensor signal' is already a known issue.)

....one more observation to conclude - it seems that the MSG adapts to the diode or the LMM .
Immediately after switching from the diode to the LMM, the engine actually performs best - meaning it sprints in the lower RPM range, and the boost pressure is also good in the mid-range. It sprints smoothly. After driving for a bit, everything goes back to being boring as usual with the LMM .

was everything understandable?

Hi,

pics of what? Of the diode? Or of an alternative circuit? I haven't thought about an alternative yet.
I absolutely cannot understand the observations you describe, that the engine performs worse above 2000 RPM. The ignition timing and fuel injection volume are not affected by the diode above approximately 1500 RPM. It's possible that the onset of torque, which occurs slightly below 2000 RPM, is not as noticeable subjectively because the change in acceleration is somewhat smaller.
The only change I've noticed is the increased fuel injection amount at speeds below 1500 RPM, which results in better throttle response, but also a little bit of black smoke. Otherwise, everything is the same.
Have you already activated your AGR (Abgasrückführung)? And what kind of engine do you have?

Best regards, Matthias.

Okay, agr is too - it's not about the diode - I already described that - the idea of driving with it permanently is a joke - for 20km, the msg will put you in emergency mode 4 times .
'And as I said, this isn't a subjective feeling that the engine performs less well in the mid-range; you can see where it's coming from – a drop in boost pressure. It's supposed to be 2.5 bar, but it's at 2.34 bar (absolute). Actually, what's happening is that the overboosts are getting worse, which is why it's so noticeable. There are pressure fluctuations of 0.4 bar in the mid-range, and you can definitely feel that.'
motörle: arl
and that.
That's certainly an idea. In principle, it should be sufficient if I create a specific resistance in parallel with the sensor (i.e., from +5V to the signal line).
I meant modifications or adjustments using pictures or image editing.

No, regarding the crafting project, I simply haven't found the time for it yet. As soon as I have any results, I will definitely share them here.
During my test drives, I didn't observe any noticeable pressure drops or other issues. The logs showing the correlation between the mass airflow sensor (MAF) and the glow plug relay should be somewhere in this forum. The only difference I noticed was that the car ran within the soot limit using the MAF sensor up to approximately 1500 RPM. Beyond that, the behavior was the same whether using the MAF or the glow plug relay.
The 'EGR Range exceeded' error triggers the yellow engine warning light when a diode is used, but it does not result in a limp mode. The behavior is the same before and after the error message appears.

Best regards, Matthias.

Hello Matt,

Are you driving with a faulty AGR valve? Or what? If so, shouldn't you always have a warning light on?

I, for one, tackled the problem mechanically! I ripped out the small grid located in front of the actual sensor element of the mass airflow sensor. Then, the car became very erratic and unpredictable; it sputtered unacceptably when shifting and starting, and there was an error code indicating an excessively high measured air mass. So, I improvised a new grid using a piece of mosquito netting, the kind you find on windows. Now, there's hardly any sputtering, no error code, and the acceleration is very convincing, spontaneous, and consistent.

You can definitely test different replacement grates until you find one that matches the level of cloudiness.

'Question for clarification? The more you try to manipulate the EGR system when it's functioning correctly, the more aggressively it would be controlled to adjust the mass airflow sensor (MAF) value, and thus the apparent EGR rate, in the 'correct' direction?'

@BesidesMom
If only the AGR (Abgasrückführung - Exhaust Gas Recirculation) is deactivated, then the deviation from the target value is apparently not large enough to trigger an error message. However, I have adjusted the target value on 'Adjustment' -> Channel 3 as high as possible.
So far, the 'EGR Range exceeded' or similar error message has only appeared once. After a few engine starts, the light went off again. The error code was then stored in the system with the note 'sporadic.'

When using the diode, an 'implausible LMM signal' error message immediately appears. However, this does not cause the lamp to light up.
However, the deviation from the AGR (Abgasrückführung - exhaust gas recirculation) system's normal operation is now definitely beyond the acceptable range - the warning light comes on with every engine start, but the engine runs normally.
AGR errors always occur during acceleration. I still need to analyze the data from the test drives I conducted, and I'll see if I can learn anything from it.

Due to this problem, this thread exists; otherwise, this issue would never have prompted me .

Can you explain the 'due to excessive measured air mass' error in more detail? Did you then receive an AGR (Exhaust Gas Recirculation) error?
What kind of small grid are you talking about? I only know about the large one that's inside the intake manifold, or have I never noticed that small one?
Why did your acceleration change? When operating in a stationary state and exceeding 1500 RPM, the acceleration shouldn't change due to different mass airflow sensor (MAF) values, because you're not operating within the soot reduction range anyway.

Regarding your question about understanding: You are correct that even with a too-high (although the actual value is lower) mass airflow rate (MAF), the system will still try to regulate to the target MAF value. Consequently, the actual exhaust gas recirculation (EGR) rate will be higher.

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

'Note:'
During brief tests with a 2002 Passat equipped with the AWX engine, I noticed that the intersection point of soot and torque limits is lower. The mass airflow sensor (MAF) values are also slightly higher. When the engine is idling roughly, you can see a bit of soot if you stand next to the exhaust. This isn't the case with mine. A 2004 ASZ engine in a Fabia also seems to have the same low values as mine.
According to the records, the 2002 Passat has a different mass airflow sensor (MAF sensor), specifically part number 071 906 461 A or AX. Does anyone have any information about this?

Best regards,
Matthias

PS: Actually, all of this is just pointless chatter. What would actually be useful is adjusting the corresponding parameter maps in the engine control unit (ECU). Unfortunately, I don't have access to something like that .

Hello Matt,

For me, it was the ARL engine. Adjusting the AGR rate didn't help in my case; the error appeared, just as you described, after a few kilometers of partial load.

After I deactivated the AGR (Abgasrückführung), I finally had a VTG (Variable Geometry Turbocharger) turbocharger. Before that, the car was just a waste. There was a horrible thud in the lower back at 2000 rpm, and before that, it was completely flat. Only the 'Boh ey' crowd might like that. Most of the time, I drive it at very low RPMs and partial load, and I want smooth, consistent acceleration.

My LMM (Laminar Flow Meter) was a piece of tubing that also contained a small section of tubing in the direction of flow. The sensor plate was located inside this small section. This small section of tubing had a very thick, specially designed plastic grid in front of the sensor, presumably to protect it from potential impacts. However, from a physical perspective, this doesn't make much sense, so I assumed it must have something to do with homogenizing the airflow within the sensor tube.

'Because this small, restrictive grid in front of the sensor tube, when measured against the open, larger tube, only allows a disproportionately small and unrepresentative portion of the air mass to pass through, I had expected to find an extremely sensitive characteristic. Which, indeed, was the case, because after removing the small grid, the vehicle reacted to a gas surge with a cloud, and an error was logged in the MSG (which I haven't checked). After installing a fine mesh screen in front of the small sensor tube, the right compromise was found.'

Effect: A sudden, aggressive, and immediate response to the accelerator pedal.
(Of course, the throttle remained unaffected because we were already in the torque limit mode. But that first second counts ).