I would like to hear your opinion on this, as this is a first for me...
The following capture was made on a MAF from a 2008 Citroen Berlingo 1.6 HDI.
Don't have the engine code at hand, but I can write it later in here...
Blue channel (A) is the scoped signal wire from the MAF. Inverted frequency type signal, as I have seen in other PSA engines.
Red channel (B) represents the current on the 12 volt feed wire, using a low current probe (450 mA).
Black is a math channel that represents the negative value of the frequency of channel A. I use the negative value of the frequency in here, just for simplicity. The point is to have an increase in airflow to be represented as an increase in frequency.
As you can see clearly, there are some high frequency events that are very strange (at least for me). Completely non linear to the direct current measurement. This high frequency peaks, seems to happen at the same time that theoretically we should have the lowest airflow.
There is a strange increase in current in that event, that I'm not sure if it is related or not to the current of the hot wire. Don't know...
This events are not present at higher airflow levels.
If you want to look at the actual signal when the high frequency event is present:
So, my question is, can this be normal? Have you seen it before?
The MAF electronics could be designed in a way, that it could produce a non linear frequency measurement, at lower airflow. I believe that is possible...
In the waveform library I could only found one MAF measurement that is likely to be the same engine as this.
The thing is that it doesn't contain a measurement at idle. The lowest RPM in the waveform is 1500, and the high frequency event is not present.
I could compare the frequency at the highest RPM, 1.045 khz, very close to the value I'm getting.
The owner of the vehicle only says that it kinda looks like the engine is a little bit out of performance, but he admits that he may be wrong, because he only drives that van once per week, and switching from one car to another could give that impression.
I didn't do a serial data reading of the MAF g/s PID, but most likely I will when I get the chance. Unfortunately Pico software doesn't allow me to that (yet)