OBDlink MX+ and OBD Fusion app readings

Not sure if anyone with this setup but I am getting my fuel readings wrong. See pictures. I am told by the OBD Fusion app support folks that this is the value what the app is receiving from the fuel tank sensor? That does not make any sense.

In the OBD Fusion app configuration I setup up the fuel tank size to 38 Gal, the tank is full and yet the app reads at 34.87 Gal and 92.94% fuel remaining volume. Something is way off.

Should I even trust this app readings all together?

 

Some things monitored are calculated and not exact this maybe one of those things.

 

Mine reads the same. However, from my testing it's pretty darn close to what's in the tank +/- a gal. There is supposedly 6-8 gal reserve in the tank after the "0 miles" warning on the dash. Using that display, I've run the tank down to presumedly 2.5 gal without issue outside of a slight sputter on startup the next morning on my steeper driveway. When I went for gas, it took 35 gal to fill it up.

 

The fuel level sensor is a variable resistor attached to the sending unit in the fuel tank. It send a resistance signal directly into the instrument cluster to run the fuel tank level gauge.

The cluster has a smoothing algorithm built it to read the data. As you drive the fuel sloshes around and the readings are all over the place if you look directly at the sensor.

The instrument cluster reports the fuel level in liters out to the other ecus on the network. I wonder if OBD Fusion just has a scaling issues or what they are using for the data source.

I have the app and can do some testing to see what they are doing. Good chance a custom PID can be programmed into the app to get a more accurate reading.