Electronic Correction for Aging LMM Devices (Articles)

Hello everyone,

Based on the characteristic curves for the Bosch mass airflow sensor (MAF), it can be seen that in the upper measurement range, a higher air flow rate results in a relatively small increase in the MAF measurement voltage.
Conversely, a slight decrease in the mass flow sensor's measured voltage (due to aging of the sensor) initially appears to the engine control unit as a significant loss of airflow within the upper measurement range. This, in turn, leads to a substantial reduction in fuel injection volume and consequently results in a corresponding power loss.

As a possible correction, it might be sufficient to increase the output voltage of the LMM (likely referring to a specific device or circuit) by a constant amount across the entire measurement range. This can again be achieved with a relatively simple circuit, which I'm attaching here as a preliminary design (it's an emitter follower configured to provide a higher voltage).
This should compensate for performance losses caused by aging mass airflow sensors, allowing the sensor to be used for a longer period. The trimmer allows you to adjust the voltage gain from 0 to approximately 0.6 volts.

A gain of 0.6 volts in the measured voltage corresponds to an air mass (backflow) gain of approximately 400 mg per cycle at the Pmax point, and approximately 300 mg per cycle at idle.
The latter could, in turn, lead to an excessively high EGR rate, so the turbocharger should only be revved up as much as necessary to just reach the full power output or the target air mass value within the Pmax range (as measured by VAGCOM). Additionally, the adaptation possibility in the EGR channel can be utilized to favor a maximum air mass.

The cables to be tapped (pins on the MAF sensor connector) are:
+5 Volts: In a Bosch mass airflow sensor (MAF), the value is 4; in a Pierburg MAF, it's 1.
Sensor mass: for Bosch Mass Air Flow (MAF) sensors = 3, for Pierburg MAF sensors = 2.
LMM reading / Output: For the Bosch LMM sensor, the value is 5; for the Pierburg LMM sensor, the value is 6.

Regarding the value of R2:
Starting with a resistance of 4.7 kΩ, plug in an appropriate resistor into the mass airflow sensor (MAF) connector between +5V and the measurement terminal. With the ignition turned on, you should measure a voltage of approximately 0.7 volts across the resistor. If the voltage is higher, decrease the resistor value; if it's lower, increase the value until you achieve 0.7 volts as accurately as possible. Use this value as R2; try not to go below 2.2 kΩ.

The circuit has not yet been tested in practice, because the mass airflow sensors (LMM) in our TDIs are still working fine, and I haven't been able to find a test subject whose LMM is broken enough.

I cannot assume any liability for potential damages resulting from the use of this circuit.

If someone with an LMM (Lambda Multi Monitor) issue is still willing to test the circuit in practice, it would be interesting to obtain the corresponding VAGCOM air mass readings both without and with the additional circuit (ideally at idle without EGR active and at full load around 4000 rpm).

Hi Ulf.

If my interface finally arrives, I could take measurements and maybe even try out your circuit.

But since I don't know if my LLM is "old," I also don't know if I'm suitable to be a test subject.

Where are you from in the Saarland? I'm currently in Cologne and sometimes drive to the Eifel region (which goes through the Saarland).

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.

dieselmartin wrote:

But since I don't know if my LMM is "old," I also don't know if I would be suitable as a test subject.

Hi.

As long as a car isn't noticeably slow due to the engine management system (e.g., poor maximum speed or bad acceleration time), you don't really need to worry about the transmission.

I live in Kleinblittersdorf, right next to Saarbrücken (Germany).

Hello Ulf!

Once again, brilliant!

Unfortunately, not everyone has a VAGCOM. I did the test with the diode today, based on your article. And sure enough, the error that occurs during acceleration is no longer present. So it's definitely the MAF sensor.

"Of course, I'm very interested in your circuit. However, I don't happen to have a VAGCOM device. But I think I can get closer to the correct setting in another way. When accelerating fully in 5th gear, with the mass airflow sensor (MAF) working, I saw an instantaneous fuel consumption of 13.7 l/100km on the MFA display from around 2000 rpm, which is full torque. The same value appeared again when the diode was activated. With my faulty MAF sensor, this value fluctuates between approximately 10.7 and 13.2 l/100km. Therefore, I should adjust the value in the balancing circuit so that I reach 13.7 l/100km again."

Do you agree with me on that?

mcgregg

If you're interested, I can send you a defective Bosch mass airflow sensor from an AJM pump-injector engine!
Then you can test it extensively!
It's just gathering dust here anyway...

Best regards,
Daniel.

mcgregg wrote:

When accelerating fully in 5th gear, with the mass airflow sensor (MAF) functioning correctly, I saw an instantaneous fuel consumption of 13.7 liters per 100 km on the MFA (multifunction display), starting around 2000 RPM, which is full torque. The same value reappeared when using the diode setting. With my defective MAF sensor, this value fluctuates between approximately 10.7 and 13.2 liters per 100 km. Therefore, I need to adjust the value in the balancing circuit so that I reach exactly 13.7 liters per 100 km again. Do you agree with me on that?

Hi.

In theory, that should work, in my opinion.
The rest is up to you... but please tell us how it turns out.

Dan.jel wrote:

If you are interested, I can send you a defective Bosch mass airflow sensor from an AJM pump nozzle engine! Then you can test it extensively!

Hi Danjel,

Thank you for your offer, but for the tests, I would need to use my wife's Ibiza because my tractor still has the Pierburg mass airflow sensor.

Since testing the circuit can only be done by opening and tapping into the MAF sensor wiring harness, it would once again cause some minor family-related disagreements, because I generally don't have access to the Seat as a research laboratory.

Perhaps I can convince a colleague with an ASV Octavia to try it. His mass airflow sensor (MAF) is already showing signs of degradation after over 80,000 km, making him a suitable candidate...

Hello Ulf,

I had a similar circuit installed to adjust my old, faulty mass airflow sensor (MAF). Now I have a new MAF sensor installed.

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

As far as I could tell from my own experience, apart from the maximum value, the measurement during acceleration is also important. Simply amplifying the entire signal leads to the same effect as with the diode solution – the car escapes its own cloud of soot. However, the effect is enormous, especially when overcoming turbo lag.

My solution:

Reduce the signal from the mass airflow sensor (MAF) by approximately 0.7 V using a diode, and then readjust the amplification so that the same voltage is output at idle (engine off) as before. The effect of the diode can be further adjusted using a parallel resistor.
This ensures that the voltage curve in the lower range of the air mass measurement does not deviate significantly from the target value, and it produces less soot during acceleration.

Bei Vollgas ( mit entsprechendem Ladedruck ) darf er aus meiner Sicht beliebig viel Luftmasse messen, da sich die max. Einspritzmenge über das MSG von selbst begrenzt. ( Fest programmierte max. Injection volume.
If you haven't adjusted anything else related to the fuel injection amount, then this won't cause the engine to produce excessive soot during full throttle!
I could fax/scan a sketch of my circuit and send it to you.

garth.brooks wrote:

Hello Ulf, I had a similar circuit installed to adjust my old, faulty mass airflow sensor (MAF). Now I have a new MAF sensor installed. I used an operational amplifier, but it does the same thing as your transistor.

Hi Garth,
In my design, I placed the highest priority on safety: even in the event of a failure, the Mass Air Flow (MAF) sensor input to the engine control unit will receive at most 5 volts, which it should still be able to handle without issues.

If your (undoubtedly much more flexible!) operating system solution is powered by 12 volts, those signals could potentially also be applied to the MAF sensor input – and I'm not sure if the engine control unit would handle that without some kind of partial failure...

If you can suggest a practical operational amplifier that can provide a stable 4.5 volts at the output while being powered by a 5-volt supply, I would try to build a complete mass airflow sensor replacement based on intake manifold pressure, pedal position (and possibly also the EGR control, to make it completely realistic ).

Quote:

I could fax/scan a sketch of my circuit and send it to you.

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

Hello Ulf,

I had a similar circuit installed to adjust my old, faulty mass airflow sensor (MAF). Now I have a new MAF sensor installed.

I actually used an operational amplifier, but it does the same thing as your transistor.
Hi Garth,
In my design, I placed the highest priority on safety: even in the event of a failure, the Mass Air Flow (MAF) sensor input to the engine control unit will receive at most 5 volts, which it should still be able to handle without issues.

If your (undoubtedly much more flexible!) operating system solution is powered by 12 volts, those signals could potentially also be applied to the MAF sensor input – and I'm not sure if the engine control unit would handle that without some kind of partial failure...

If you can recommend a practical operational amplifier that can provide a stable 4.5 volts at the output when supplied with 5 volts, I would try to build a complete mass airflow sensor replacement based on intake manifold pressure, pedal position (and possibly also EGR control ) to make it completely realistic.

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


Ulf, you're the best!

How about using an overvoltage protection (OVP) device and a 5.1V Zener diode as protection at the output, connected towards the engine control unit?

'Your fake would be brilliant. In such a case, however, one could solve this using a microcontroller and potentially intervene specifically to perfectly manipulate the output signal, right?'

joergs wrote:

How about an overvoltage protection (OVP) and a 5.1V Zener diode as protection at the output, connected towards the engine control unit?

Hi Jörg,
Here's my radical opinion: A voltage that doesn't even enter my circuit is, without a doubt, the safest option. Even a Zener diode can fail (due to a loose solder joint or something similar). Granted, the probability of this happening is very low, but still...

Quote:

your fake would be brilliant. In such a case, however, one could solve this using a microcontroller and potentially intervene specifically to perfectly manipulate the output signal or?

Theoretically, yes. However, programmable digital projects are not my area of expertise due to a lack of experience (and time to delve into them), so I leave those to others.

I either want to achieve it purely through analog methods (using a physical dial and thumb), or I'll abandon the project altogether.

How about an overvoltage protection (OVP) and a 5.1V Zener diode as protection at the output, connected to the engine control unit?
Hi Jörg,
Here's my radical opinion: A voltage that doesn't even enter my circuit is, without a doubt, the safest option. Even a Zener diode can fail (due to a loose solder joint or something similar). Granted, the probability of this happening is very low, but still...

your fake would be brilliant. In such a case, however, one could solve this using a microcontroller and potentially intervene specifically to perfectly manipulate the output signal or?
Theoretically, yes. However, programmable digital projects are not really my area of expertise due to a lack of experience (and time to get into them), so I leave those to others.

I either want to achieve it purely through analog methods (e.g., using a ruler and calculations), or I'll abandon the project...

Okay, while I can understand how the Z-diode works, the probability that this scenario will actually occur is quite low!

Well, as for microcontrollers, I completely agree with you. It's not everyone's cup of tea. And the challenges can be quite significant!

@everyone
Wasn't there anyone here who was familiar with microcontroller programming??? That would be a great project to work on!

garth.brooks wrote:

As far as I could tell from my own experience, apart from the full-throttle value, the measurement during acceleration is also important. Simply amplifying the signal as a whole leads to the same effect as with the diode solution - The car escapes its own cloud of soot - However, the effect, especially when overcoming turbo lag, is enormous.

Hi Garth,

I missed something earlier...
In my AFN (air fuel nozzle), the diode solution produced very little smoke (although "very little" is, of course, highly subjective). I only saw a bit of smoke once, reflected in the rearview mirror against the low-hanging sun, when I was performing full-throttle acceleration tests starting almost from idle speed.
According to the VAGCOM readings, the mass airflow rate (LMM) was constantly at 1275 mg/hub, which is equivalent to having full boost pressure applied all the time.

When shifting the LMM signal, even with an increased LMM value, the motor computer will not constantly report a "bursting" cylinder fill (because the LMM voltage still somewhat follows the actual mass flow), so the soot problem is probably less likely to occur compared to using a diode.

Furthermore, the soot can be removed using a trimmer - although this may result in a slight loss of performance .

Hi Ulf,

'Rail to Rail' refers to op-amps that can operate up to 5 volts. However, you don't need that. In my case, a standard 741/OP2 was used, which is sufficient for 1000mg. The engine control unit won't accept more anyway, because the maximum injection amount limit will be reached before that.

Of course it's running at 5 volts; otherwise, every short voltage spike would destroy my motor controller.

I wouldn't rely on a 5-volt Zener diode either; it might be too slow to protect a sensitive ADC (Analog-to-Digital Converter).

I'm going to try to recall the circuit diagram today and send it to you later.
Ich hatte das Ganze in Feiflugverdrahtung in den abgezwicken Kabelbaum gelötet, und mit Harz gegen wasauchimmer geschützt. Mußte ja wieder fahren können bis ein neuer LMM besorgt war. Das Ganze sauber mit Schrumpfschlauch überzogen. FällIt doesn't even turn on.

That's how I saved money on the expensive original plugs.

Hello again,

After Garth emailed me his circuit diagram, and I redrew and resized it as a JPG, I've also attached the original version.

The advantage is the adjustable gain, and that lower mass airflow (LMM) values are amplified less or even reduced by the diode, which reduces soot formation when switching from partial to full load and improves the chances of passing the emissions test.

As an operational amplifier (op amp), I have specified a low-voltage type that can reliably output up to 4.8 volts when supplied with 5 volts.
According to datasheets of other, more "standard" operational amplifiers, this is not always the case, but Garth's experiences suggest that even common ICs can deliver the desired results.

Hi Ulf,

I also have three faulty mass airflow sensors lying around.

A 90 hp TDI engine from a Volkswagen Golf 4 (I don't know the exact engine code right now).
and another one from my A6 AFN, but unfortunately, that one is also...
'Another new one from Bosch.'
And then there's one from a Volkswagen Golf 3 1Z - that's a Pierburg part.

If you can make use of it, I'd be happy to give it to you for free.
Please provide the text you would like me to translate from German to English. I will then give you only the translation, without any explanations.

Regards,
arne