Integrating with a car's CPU

It is proprietary information. Your choices are either to remove the engine ECU completely and install a programmable aftermarket controller, or to reverse-engineer the ECU yourself.

There are some more common ECU modules out there which have been reverse engineered pretty well by the aftermarket tuner community, but those guys are also not generally very talkative.

--scott

Ok, I'm a bit familiar with the fuel dispensing technologies and as far as I know, In AVI devices the fuel tank ring reads the odometer and transmits it to the system (via Wi-Fi or RFID). If I'm not mistaken AVI devices could be integrate in almost any model of car... So from where do they receive the odometer information?

Probably from the computer that controls the instruments, which usually gets a pulse from transmission which it derives speed and distance from.

Many of the newer cars have data busses rather than individual lines going from one black box to another. This means you can add a device to the data buss and extract data from all the different computers throughout the vehicle.

--scott