Draft: Electronic Correction for Aging LMM (Articles)

Hello everyone,

Based on the characteristics of the Bosch LMM, it can be seen that in the upper measurement range, a higher throughput results in a relatively small increase in the LMM measurement voltage.
Conversely, this means that a slight decrease in the LMM (lambda sensor) measuring voltage (due to aging) appears as a significant loss of airflow to the MSG (mass airflow sensor) initially in the upper measuring range. This, in turn, causes a strong reduction in the amount of fuel injected, and thus a corresponding loss of power.

As a rough correction, it might be sufficient to simply raise the LMM output voltage by a constant amount over the entire measurement range. This simple circuit is sufficient, which I have attached in the design here (= emitter follower in the direction of higher voltage).
This should allow for compensation for performance losses due to aging LMMs, so that the LMM can be operated for a longer period. The trimmer allows you to adjust the voltage gain from 0 to approximately 0.6 volts.

0.6 Volt corresponds to a gain in the measured voltage, with a measured air mass recovery of approximately 400 mg/stroke in the Pmax range, and approximately 300 mg/stroke at idle.
The latter could, in turn, lead to an excessively high AGR (Air-Fuel Ratio) rate, so that the trimmer should only be adjusted so far that the full power or the target air mass value in the Pmax range (VAGCOM measurement) is just reached. Additionally, it is possible to utilize the adaptability in the AGR (Air-Gas Ratio) channel to achieve maximum air mass.

The cables to be connected (pins on the LMM connector) are
+ 5 Volt: Bosch-LMM = 4, Pierburg-LMM = 1
Sensor Mass: Bosch-LMM = 3, Pierburg-LMM = 2
LMM Measurement / Ausgang: Bosch LMM = 5, Pierburg LMM = 6

For the R2 value:
Start with a 4.7 kΩ resistor, then connect a corresponding resistor at the LMM connector between +5V and the measurement terminal. When the ignition is on, you should measure approximately 0.7V across the resistor. If the voltage is higher, reduce the resistor value. If the voltage is lower, increase the value, until the 0.7V is achieved as accurately as possible. Incorporate this value as R2; the value should not be less than 2.2 kOhm.

The circuit has not yet been tested in practice, because the LMMs in our TDIs are still functioning correctly, and I have not yet been able to engage a test pilot whose LMM is faulty enough.

For possible I cannot assume any liability for damage resulting from the use of the circuit!

If a LMM-damaged party is still willing to test the circuit in practice, the corresponding VAGCOM air mass values, both with and without the additional circuit, would also be of interest (preferably at idle without AGR and at full load at 4000 rpm).

[Translating...]

Hi ulf

wenn mein INterface endlich mal ankommen wuerde, koennte ich messen und evtl. auch deine Schaltung versuchen.

Aber da ich nicht weiss, ob mein LMM "alt" ist, weiss ich auch nicht, ob ich als Versuch-Kaninchen tauge.

Wo ausm Saarland bist du denn ??? Ich hocke in KL und fahr abundzu in die Eifel (also durchs Saarland)

m;

[Translating...]

dieselmartin wrote:

Aber da ich nicht weiss, ob mein LMM "alt" ist, weiss ich auch nicht, ob ich als Versuch-Kaninchen tauge.

Hi

solange ein Wagen nicht vom LMM her auffällig lahmt (Vmax bzw. DZR-Zeit mies), braucht man die Schaltung eh nicht.

Ich wohne in Kleinblittersdorf , direkt neben Saargemünd (F).

[Translating...]

Hallo Ulf!

Mal wieder genial!

Nur leider hat nicht jeder VAGCOM. Ich habe heute, aufgrund Deines Artikels heute mal den Test mit der Diode gemacht. Und siehe da, der Fehler beim Beschleunigen tritt nicht mehr auf. Also eindeutig der LMM.

Nun bin ich an Deiner Schaltung natürlich sehr interessiert. Nur habe ich "zufällig" kein VAGCOM. Ich denke aber, ich kann mich dem richtigen Einstellwert auf andere Art nähern. Beim vollen Beschleunigen im 5. Gang hatte ich bei funktionierendem LMM ab ca. 2000 U/min, also vollem Drehmoment, auf der MFA einen Momentanverbrauch von 13,7 l/100km. Der gleiche Wert hat sich auch wieder bei der Diode eingestellt. Bei meinem defekten LMM schwnkt dieser Wert zwischen ca. 10,7 und 13,2 l/100 km. Demnach müßte ich bei der Ausgleichsschaltung den Wert so einstellen, daß ich 13,7 l/100km gerade wieder erreiche.

Stimmst Du mir da zu?

mcgregg

[Translating...]Bei Interesse kann ich Dir einen defekten Bosch-LMM aus nem AJM Pumpe Düse zuschicken!
Dann kannste ausgiebig testen!
Liegt bei mir sowieso nur rum...

Liebe Grüße,
Dan.jel

[Translating...]

mcgregg wrote:

Beim vollen Beschleunigen im 5. Gang hatte ich bei funktionierendem LMM ab ca. 2000 U/min, also vollem Drehmoment, auf der MFA einen Momentanverbrauch von 13,7 l/100km. Der gleiche Wert hat sich auch wieder bei der Diode eingestellt. Bei meinem defekten LMM schwnkt dieser Wert zwischen ca. 10,7 und 13,2 l/100 km. Demnach müßte ich bei der Ausgleichsschaltung den Wert so einstellen, daß ich 13,7 l/100km gerade wieder erreiche. Stimmst Du mir da zu?

Hi

in der Theorie müßte das IMO funzen.
Die Praxis bleibt dann Dir überlassen . . . aber erzähl uns bitte, wie es ausgegangen ist.

[Translating...]

Dan.jel wrote:

Bei Interesse kann ich Dir einen defekten Bosch-LMM aus nem AJM Pumpe Düse zuschicken! Dann kannste ausgiebig testen!

Hi Danjel,

danke für Dein Angebot, aber für Tests müßte ich den Ibiza meiner besseren Hälfte nehmen,denn mein Trecker hat noch den Pierburg-LMM.

Da ein Test der Schaltung nur mit Öffnen und Anzapfen des LMM-Kabelstranges möglich ist, gäbe das mal wieder leichte familiäre Kimaverschiebungen, denn auf den Seat als Forschungslabor habe ich grundsätzlich keinen Zugriff . . .

Aber vielleicht kann ich einem Kollegen mit einem ASV-Octavia die Schaltung schmackhaft machen. Dessen LMM ist mit über 80Tkm schon deutlich auf dem absteigenden Ast und von daher ein geeigneter Kandidat . . .

Hello Ulf,

I had a circuit like that in order to adapt my old, defective O2 sensor. Currently, a new LMM is in place.

I actually used an operational amplifier, but it does the same thing as your transistor.

As far as I can assess, in addition to the full-throttle value, measuring during acceleration is also important. Simply amplifying the signal as a whole has the same effect as the diode solution - The car escapes its own exhaust cloud - However, the effect is particularly noticeable when overcoming the turbo lag.

My solution. :

Signal from the LMM with a diode reducing the voltage by 0.7V, and then adjust the gain again so that the same voltage as before is output in the (motor) idle state. The effect of the diode can still be adjusted using a parallel resistor.
This prevents the pressure curve in the lower range of the air mass measurement from deviating so significantly from the target value, resulting in less black smoke when accelerating.

At full throttle (with the corresponding boost pressure), he should be able to measure an arbitrarily large amount of air mass, as the maximum injection amount is limited by the MSG itself. (Pre-programmed maximum). (Injection amount)
'Therefore, anyone who hasn't adjusted the fuel injection amount will not reach the full throttle soot area!'
I could send you a sketch of my circuit via fax / scan.

garth.brooks wrote:

Hello Ulf, I had a circuit like that in order to adapt my old, defective O2 sensor. Currently, a new LMM is in place. However, I used an operational amplifier, which does the same thing as your transistor.

Hi Garth,
In my setup, I have prioritized safety above all else: even in the event of a failure, the LMM input of the engine computer should receive a maximum of 5 volts, which it should be able to handle without any problems.

If your (definitely much more flexible!) surgical solution is powered by 12 volts, then in the worst case, they could also be applied to the LMM input - and I don't know if the motor computer will tolerate this without some intervention . . .

If you could suggest a practical, off-the-shelf OP (operational amplifier) that can provide stable 4.5V at the output when powered by 5V, I would try to build a complete LMM (Linear Mass Airflow) replacement based on the intake air pressure, pedal voltage (and possibly also the AGR (Aspiration Gas Recirculation) control signal, to complete the system ).

Quote:

I could fax/scan you a sketch of my circuit.

I don't have a fax machine, but scanning and emailing would be perfect

Hello Ulf,

I had a circuit like that in order to adapt my old, defective O2 sensor. Currently, a new LMM is in place.

However, I used an operational amplifier, which does the same thing as your transistor.
Hi Garth,
In my setup, I have prioritized safety above all else: even in the event of a failure, the LMM input of the engine computer should receive a maximum of 5 volts, which it should be able to handle without any problems.

If your (definitely much more flexible!) surgical solution is powered by 12 volts, then in the worst case, they could also be applied to the LMM input - and I don't know if the motor computer will tolerate this without some intervention . . .

If you could suggest a practical, off-the-shelf OP (operational amplifier) that can provide stable 4.5V at the output when powered by 5V, I would try to build a complete LMM (Linear Mass Airflow) replacement based on the intake air pressure, pedal voltage (and possibly also the AGR (Aspiration Gas Recirculation) control signal, to complete the system ).

I could fax/scan you a sketch of my circuit.
I don't have a fax machine, but scanning and emailing would be perfect


ulf, you're the best!

How about adding an OV (overvoltage) and AM (overcurrent) protection diode at the output towards the engine control unit (ECU)?

your fake would be amazing. in such a case, one could solve this all with a microcontroller and potentially intervene specifically and perfectly manipulate the output signal or?

joergs wrote:

How about adding an OV (overvoltage) protection and a 5.1V Z-diode at the output towards the ECU (Engine Control Unit)?

Hi Jörg
That's my radical approach: a voltage that doesn't even enter my circuit is, by definition, the safest. Even a Z-diode can fail (due to a loose solder joint, for example). While the probability is very low, but still...

Quote:

Your fake would be amazing. In such a case, one could potentially solve everything with a microcontroller and, in turn, be able to specifically intervene and perfectly manipulate the output signal or?

Theoretically, yes. But programmable digital projects, due to a lack of experience (and the time required to acquire it), are not my area of expertise, and I prefer to leave them to others.

I want to either achieve this purely analog (Pi x thumb), or I will abandon the project. . . .

How about adding an OV (overvoltage) protection and a 5.1V Z-diode at the output towards the engine control unit (ECU) as a protection?
Hi Jörg
That's my radical approach: a voltage that doesn't even enter my circuit is, by definition, the safest. Even a Z-diode can fail (due to a loose solder joint, for example). While the probability is very low, but still...

Your fake would be amazing. In such a case, one could potentially solve everything with a microcontroller and, in turn, be able to specifically intervene and perfectly manipulate the output signal or?
Theoretically, yes. But programmable digital projects, due to a lack of experience (and the time required to acquire it), are not my area of expertise, and I prefer to leave them to others.

I want to either achieve this purely analog (Pi x thumb), or I'll abandon the project. . .

'While I can understand the Z-diode, the probability that the drop will occur is actually quite low!'

Well, regarding microcontrollers, I completely agree with you. It's not for everyone. And the potential pitfalls can be quite significant!

@all
Was, niemand hier, der sich mit der Programmierung von Mikrocontrollern auskennt? Das wäre doch eine tolle Möglichkeit, sich auszutoben!

garth.brooks wrote:

As far as I can assess, in addition to the full-throttle value, measuring during acceleration is also important. Simply amplifying the signal as a whole has the same effect as the diode solution - The car escapes its own exhaust cloud - However, the effect is particularly noticeable when overcoming the turbo lag.

Hi Garth,

I missed something earlier...
In my AFN, the diode solution produced very little smoke (although "very little" is, of course, highly subjective) - I only saw a small amount of smoke once, when I was practically accelerating from idle speed in full throttle, looking directly at the sun in the rearview mirror (!).
According to VAGCOM, the LMM value was constantly 1275 mg/stroke - which is as if the full boost pressure was always present.

However, when using the LMM signal to move the throttle, the increased LMM value is not constantly reporting a "failing cylinder fill" to the engine computer (because the LMM voltage still somehow follows the actual mass flow), so that, IMO, the soot problem is likely to be less than with the diode.

Furthermore, you can also remove the soot with a trimmer - however, this may then result in a slight decrease in performance

Hi Ulf,

The op-amps that operate up to 5 volts are called 'Rail to Rail', but you don't need that information. I had a standard 741/OP2 in there, which is sufficient for 1000mA - the control unit doesn't accept anything more because the maximum value is set beforehand. Fuel injection quantity limitation is in effect.

Of course, it's running on 5 volts, otherwise even the slightest fluctuations will destroy my motor controller.

I wouldn't rely on a 5-volt Zener diode either, as it might be too slow to protect a sensitive ADC.

I'm going to try to remember the circuit today, and then I'll send it to you.
I had soldered the entire thing into the frayed cable bundle, and protected it with resin against something. I had to be able to drive it again until a new LMM was available. The whole thing was then covered with shrink tubing. Doesn't it not stand out at all?

That way, I saved the expensive original plugs.

[Translating...]

Hallo nochmal,

nachdem Garth mir seine Schaltung gemailt hat und ich sie in ein jpg umgezeichnet und geschrumpft habe, hänge ich die OP-Version auch noch an.

Ihr Vorteil ist die einstellbare Verstärkung und daß niedrigere LMM-Werte durch die Diode weniger verstärkt oder sogar abgesenkt werden, was die Rußneigung beim Wechsel Teil-> Volllast verringert und die Chancen bei der AU verbessert.

Als OP hab ich einen Low-Voltage Typ eingezeichnet, dessen Ausgang bei 5 Volt Speisung sicher bis 4,8 Volt liefern kann.
Das ist laut Datenblättern anderer "normaler" OPs nicht immer so, aber Garth's Erfahrungen weisen darauf hin, daß auch Allerwelts-ICs das gewünschte Ergebnis liefern können.

[Translating...]Hi Ulf,

ich hätte auch noch drei defekte LMM rumliegen.

Einen vom 90 PS TDI ausm Golf 4 (MKB weiss ich gerad nicht)
und noch einen aus meinem A6 AFN, der ist aber leider auch
schon so ein neuer von Bosch.
Und dann noch einen vom Golf 3 1Z - das ist nen Pierburg.

Wenn Du damit was anfangen kannst würd ich Dir die kostenlos
zusenden.

Gruss,
arne