AMC Computerized Engine Control

The Computerized Engine Control or CEC system was an engine management system designed and used by American Motors and Jeep from 1980-1990, on the AMC 258 engine.

CEC was unique in that almost all of its sensors and actuators were digital; instead of the usual analog throttle position, coolant temperature, intake temperature and manifold pressure sensors, it used a set of fixed pressure- and temperature-controlled switches (as well as a wide-open throttle switch on the carburetor) to control fuel mixture and ignition timing. The only analog sensor in the system was the oxygen sensor. In other respects, it was a typical feedback carburetor system of the early 1980s, using a stepper motor to control fuel mixture and a two-stage "Sole-Vac" (which used a solenoid for one stage, and a vacuum motor for the other) to control idle speed. CEC also controlled ignition timing using information from the fuel-control section and an engine knock sensor on the intake manifold.

The CEC module itself (the most common version of which is the "AMC MCU Super-D") was built for AMC by Ford Motor Company, and worked with a Ford Duraspark ignition system. Despite being built by Ford, the CEC module is not related to the Ford EEC systems internally.

Because of the many vacuum-driven components and electrical connections in the system, CEC-equipped engines have a reputation of being hard to tune. The 49-state model of the CEC has no on-board diagnostic system, making it difficult to monitor the computer's operation without a breakout box, and the Carter BBD carburetor on most CEC-equipped models has problems with its idle circuit clogging, causing rough idle and stalling. In places where emissions testing isn't required, a popular modification is to bypass the computer and replace the BBD with a manually-tuned carburetor; also, several vendors (including Chrysler) offer retrofit kits that replace the CEC and the carburetor with fuel injection.