How do Fuel Controllers work?

I'm doing a school project and i want to know how fuel controllers, such as the Apex'i S-AFC or the HkS F con V, as examples.

Also information on Haltech computers and such would be helpful too.

Anyone wanna help me?

Find a description how an engine management system works, Bosch Motronic or similar system used by the automotive industry. The aftermarket ones works the same way but they are designed to be easier to reprogram.

Apex'i S-AFC is a piggyback system, if fools the oem box by manipulate the signals between the ECU and engine, and in this way it can be reprogrammed similar to an aftermarket system but there are limitations in this system and safety limitations can be overwritten. Usually don't work on newer (torque demanding) engine management systems.