For modern SI engines, the injection duration and its timing are one of the most important parameters which influence the mixture homogeneity, emissions, combustion efficiency, and engine response. In the present work, a simplified port fuel injection system with its driver algorithms was designed to control the injection duration and its timing. The Calibrated Dose method is used in this system instead of the stream mixing method. Therefore, the injected fuel mass is accurately computed according to the engine load, engine speed, engine operating condition, and the amount of air drawn into the engine. The system consists of a conventional port fuel injection system equipped with a micro-controller, a Throttle Position Sensor (TPS),a couple of Hall Effect Sensors (HES), load cell with its driver module, injector controller circuit, and a custom-made inlet port. The micro-controller is used to calculate the injection duration each engine cycle according to engine speed, amount of air drawn per cycle and engine load. The two HES are used to detect the injection timing and measure the engine speed. The TPS is used to monitor the throttle position angle so it can calculate the amount of air drawn into the engine at that time with respect to engine speed. The load cell and its driver module are used to measure the engine torque and consequently the brake power. The injector controller circuit is used to initiate the injection process at the perfect timing for the accurate duration.