AMC computerized engine control

The Computerized Engine Control or Computerized Emission Control (CEC) system is an engine management system designed and used by American Motors Corporation (AMC) and Jeep on 4- and 6- cylinder engines of its own manufacture from 1980 to 1990.

Operation

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 manufactured for AMC by Ford Motor Company, and worked with a Ford Duraspark ignition system. Although built by Ford, the CEC module is not related to the Ford EEC systems internally.

Maintenance

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 is not required, a popular modification is to bypass the computer and disable the BBD's Idle Servo, or replace the BBD with a manually tuned carburetor. Several vendors (including Chrysler) offer retrofit kits that replace the CEC and the carburetor with fuel injection.

External links

• Jeep Adventures Under the Hood, guide to the CEC system and how to tune it
• 4x4wire.com, the "Nutter" bypass