Microprocessor Control Unit (MCU)
The MCU is a solid-state micro-computer located on the left fender panel. It is the "brain" of the system and receives inputs and sends signals through a 24-pin connector. The MCU is capable of operating in 3 modes: Initialization, Open-Loop and Closed-Loop.
Initialization mode occurs when the engine is started. In this mode the MCU richens the fuel mixture for easy starting.
Open-Loop operation is controlled by MCU programming. Air/fuel ratio is fixed at a pre-determined level and allows good driveability at idle, moderate-to-heavy acceleration, and deceleration. Closed-Loop operation occurs when the engine is warm and vehicle is operated at light load conditions. In closed loop, the MCU controls the air/fuel mixture in response to signals from an oxygen sensor in the exhaust manifold.