Sensor Characteristics: Initial Values & Data

Hello.
I'm currently experiencing a significant loss of power (maximum speed is 140 km/h).
I suspect that the fuel injection quantity is being incorrectly calculated because the mass airflow sensor or the dual sensor (load pressure/temperature) is providing incorrect values in the control loop.

I once measured the LMM (Mass Air Flow sensor) on my workbench (approximately 1.2V without airflow, and about 3.5V with a lot of forced air). Based on that measurement, I deemed it to be working correctly. (Of course, a more precise measurement can be achieved with a defined airflow.)
Next up is the dual sensor (boost pressure/temperature).
Are there any comparison curves available in this forum that show how the initial voltages of the sensors behave in relation to the input measurement values?
This would allow me to determine whether a sensor is defective or still within acceptable limits.

I want to rule out potential sources of error such as diesel supply issues, the EGR valve, or the turbocharger, as I have already checked those components.

I am also considering purchasing a diagnostic system (software + adapter).
What diagnostic tools are recommended in this forum for those on a tight budget? It should be legal, have a proper description, and function correctly.

It would be great if I could receive answers to my questions here.
Thank you and best regards.
Franz.

Hello Franz,

The search function is usually the quickest way to find answers to your questions.
Therefore, try working with it a bit. Otherwise, you just end up writing everything multiple times.

Regarding your LD sensors, you can find the following information when using the search function:

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.

The most common diagnostic tool used in this forum is VAG-Com.
Available for purchase at this store.

http://shop.dieselschrauber.de/

In this context:
@ Rainer or Rudi

Does the LLM also have a linear characteristic curve?
If so, what is its function?
Does it change depending on the type of connected LLM? If so, mine is an LLM from ASV with Bosch number 0 280 217 121.

Best regards, Jochen.

Does the LLM also have a linear characteristic curve?
If so, what is its function?
Does it change depending on the type of connected LLM? If so, mine is an LLM from ASV with Bosch number 0 280 217 121.

Best regards, Jochen.
Hello Jochen,
The characteristic curve is not linear (see image).
The characteristic curve shown here represents only a general trend!
Your LMM should be an HFM5-4.7, but I don't have one available.
I have a characteristic curve.

Best regards,
Rudi

Here's a question about LMM (Linear Motor Module): Why is it always said to use a diode? Why not just connect the 5V directly to the signal line? The diode is only installed to then have, for example, 4.3V or 4.5V on the signal line, depending on the diode.
What is the problem with a higher voltage? Can the signal input handle it?

Devilseye503 wrote:

What is the problem with a higher voltage?

The MSG (Motor Control System) detects a fault, specifically a short circuit in the LMM (Lambda Measuring Module), and depending on the software configuration, it enters emergency mode.

@Rudi

Okay, so I can't simply determine the air mass by directly tapping into the sensor and using a two-point calibration in the logger. Well, then I have to resort to offline calculations, and I will log the transmitted voltage of the MAF (Mass Air Flow) sensor.

@Devil

I'm now strongly assuming that a 5V short circuit at the sensor after power-up would indicate an error and you would receive an error message.
Often, the initial voltages of 0V and 5V (or 12V, which is in any case the maximum sensor supply voltage that is theoretically available as an output voltage) are not used to enable a sensor diagnosis.

You also get 0V if the sensor hasn't been installed, which means you can't tell whether it's a minimum reading or a missing sensor. Therefore, it's often started at 0.5V = minimum reading (or another voltage other than 0V).

You also have a 5V reading (or sensor supply voltage) if the sensor shorts out and is defective –> therefore, you still can't determine whether it's a maximum value or a faulty sensor. With a 5V sensor, you often end up with a maximum measured value of 4.5V.

If you use a sensor that is not used for fault monitoring (e.g., additional sensors), you still have the entire supply voltage range as a signal output, unlike what was described above. However, there is no way to diagnose the connected sensor.

In the LLM simulation, the diode will output a sensor value of either 4.5V or 4.3V, which would correspond to the maximum (or nearly maximum) measurement range, but it wouldn't represent a short circuit for diagnostic purposes.

Best regards, Jochen.

[/edit] Oops, I wrote too much, and Ulf said the same thing in fewer words and much faster. Now you've heard it from two sides...

Thank you both.
and actually for me, because I would really have to figure that out myself - which leaves only one question - when is the maximum reached? I'm assuming 4.5V, since usually 0.5V is sufficient for reliable signal detection.