Microplex rebuild??

I have 2 of them for sale on ferrariads $249 each.

 

The MAP vacuum sensor in question is right below the label, mounted below the PCB. It is most likely a resistance based unit like the standalone Marelli MAP sensors (Marelli calls them APS 'Air Pressure Sensor'). The resistance measurement is based on a wheatstone bridge circuit, of the three connections one will be ground, another one the 5V input and the third one the corresponding output voltage. Marelli usually used standardized components and offered 1/2.0/2.5/3 and 5 bar devices.

If you can create a precise air vacuum in a test environment, it would be possible to test the functionality of the MAP sensor in question with a 5 Volt power supply and a multimeter, the pressure/voltage curve is quite linear. If the original sensor connot be sourced, a possible workaround would be to buy an external Marelli APS sensor with the same characteristics and wire it to the Microplex PCB.

 

There are any number of pressure transducers that could be used in a replacement circuit.

The trick to determining the original function curve is finding a functional original that isn't mounted in a car somewhere.

It's a matter of putting a functional spare together with someone with the equipment and ability to map the curve. Given the cost of these units, these days, nobody wants to tear into a functional one to test the sub-components.