The computer controls the fuel based on the program it has untill it warms up. It looks at engine temp. RPM. engine load and throttle postition to set fuel flow. After the engine warms up to operating temp. and the O2 sensor is up to temp. it goes into closed loop, at that time it adjust the fuel to 14.7 air fuel ratio by useing the O2 sensor. A lot of more things happen in there but thats the most of it in a nut shell.
