CARBURETED (5.8L MCU Vehicles Only)

The computer used in carbureted models is called the Microprocessor Control Unit (MCU). The MCU monitors engine operating conditions by receiving inputs from a series of engine switches and sensors. Control of output actuators determines fuel mixture and idle speed.

The MCU is a solid-state micro-computer located on the left fender panel. It receives input signals and sends control 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 air/fuel mixture in response to signals from the oxygen sensor.