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 disable the BBD's Idle Servo, or replace the BBD with a manually-tuned carburetor, this process is commonly known as the "Nutter Bypass" named after John Nutter, noted to be the first person to document the process. Several vendors (including Chrysler) offer retrofit kits that replace the CEC and the carburetor with fuel injection.

External links

* [http://home.sprynet.com/~dale02 Jeep Adventures Under the Hood] A detailed guide on the CEC system and how to tune it
* [http://www.4x4wire.com/jeep/tech/electrical/jn-ignition99/ The "Nutter Bypass"] method of eliminating the CEC system.


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