Hi guys,

I am currently trying to read the frequency from the OEM Evo 399 MAF as I built a flowbench for testing Group N rally restrictors and wanted to see how everything performs. I already have data from my bench but I also want to check the MAF as this reading would be more accurate for me at the moment.

Is it possible to get the frequency without having everything connected to the car? I connected the MAF Pins regarding some wiring diagrams (5V, MAP, MAF, 12V, Ground, IAT -> also in this order). I only need the frequency for now, I will add MAP + IAT data later and calculate everything according to these values for "real numbers".

How high is the voltage of the frequency output? Is it 12 or 5 volts? I wrote a script for a Raspberry that listens to a GPIO for a rising edge and also added a voltage converter (LD33CV) in front of it just to be sure it doesn't get destroyed by to high voltage. The script is capable to read up to 3 KHz on a Pi 3B+. I've read the maximum frequency for the OEM MAF is below this value. Also I would never hit these values with a restrictor, so this should be fine.

As soon as I connect the MAF signal cable to it I get no data. Any thoughts? Do I miss anything? Is the MAF broken? I tested the script with different inputs and got data.
By the way, I can measure the voltage of the MAP pin, but nothing on the IAT. Another topic maybe...

Thanks
Marius

 

I just received an Oscilloscope and tested it. I can read the frequency now And now I also know what the problem with my Raspberry was. The frequency signal is only about 50-70 mV and a Pi needs about 1 Volt to detect any rising edge.

Thought I cloud share this:


This is the general setup.




Frequency without airflow.




Frequency with a vaccum attached.


Has anyone ever measured the frequency when the car is not running and could confirm these values (about 50Hz -> edit: this was the line frequency of the power supply...)? I thought of getting a square wave to be honest

 

The Maf output is an pull to ground signal out for the MAF Unit. ( aka known as open collector )

So you have to do an Pullup Resistor to +5V at your Rasberry input... I didnt have an actual Value for the resistor, but i expect it in the Range of 47KΩ to 5KΩ...

Frequencys are in the Range of 5Hz to app 3200Hz ( No Frequency without Airflow, so no HZ without engine running )

IAT sensor is the same, needs an pullup resistor to 5V, could be in the Range 10KΩ to 2.2KΩ

 

with S2 Cams I idle @~ 40 Hz 1050rpm. The firmware has values down to 19 Hz

 

I have a pico-scope to measure things like this on vehicles. I would highly suggest it for doing things like this. You can trouble-shoot just about anything electrical with a scope.

 

Thank you! A friend gave me the exact info yesterday and I got it working with a 47kOhm pullup resistor. I will try the same for the IAT.







This is the full setup for now. I will build a proper flowbench in the next weeks.





Thank you guys for all the the Info!