The "black box" is the Electro-Hydraulic Actuator (EHA).
It does all of the fine mixture adjustment by varying the pressure in the lower chambers of the Fuel Distributor (FD). The EHA has a sufficiently wide range of adjustment that it is possible to create the situation you describe. If the two-wire plug has been attached upside down, and the polarity is reversed, the mixture will be very rich.
Try starting the engine and then disconnecting the EHA.

The ECU will ignore a faulty O2 (lambda) signal, and the coolant sensors will not change the mixture as much as you are experiencing.