Before going to the diagrams of the Wideband modication, here is a view of the differences between the Open Loop and Closed Loop fueling.
Open Loop fueling starts with the TPS and HES signals and proceeds through adjustments for air temperature, barometric pressure, etc., proceeding to a fuel pulse being injected into the engine (ignoring the Adapt box for a minute).
Closed Loop fueling is a software program that begins with an Open Loop fuel pulse but then quickly uses measured Oxygen from the exhaust (the O2 sensor) to determine whether the mixture is richer or leaner than the target set by the O2 Sensor (switch). With a bit of trial and error, it locks into a range of fuel pulses that alternate between being a bit rich and a bit lean. The Closed Loop program is an aggressive "enforcer" of the mixture specifed by the O2 sensor. In a stock system that mixture is a lean 14.7:1 (for gasoline).
The Closed Loop program also has another activity which is to compare (the Compare box) the Closed Loop result with the Open Loop calculation. Over time, if these fuel pulses are different, the Closed Loop program "teaches" the Open Loop program some adjustments (the Adapt box). This means the Open Loop program gets corrections that can take into account: fuel type (e.g. E10 or gasoline), fuel pressure, air filter restrictions, fuel injector contamination, and throttle body, valve & cylinder accumulations. A weakness of the 1150 Motronic is that it treats both cylinders equally, which means we have to manually balance (left and right cylinders) the air (TB and valves) and fuel (injector cleaning and matching).
The diagram below can give an idea of which engine modifications will have a long-term effect on engine performance and which will be "learned out" by the Motronic's Closed Loop program.
My objective with the Wideband O2 project was to leave the many functions of the Motronic intact even while richening the overall mixture.