using a air compressor on those sensors is a terrible way to test them, and can give you wrong results. The pressure at the gauge is not always the pressure at the end with those. I thought you had it on the vehicle. The scale will still be off with the 3.3bar but should not by that much.
You should be using one of these for testing a map sensor, Air compressors can also damage the diaphram on Map sensors with pressure spikes depending on the quality of the compressor and the pressure valve.
