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{{Short description|Engine management system developed by American Motors Corporation}}
{{Use dmy dates|date=February 2023}}

The '''Computerized Engine Control''' or '''Computerized Emission Control''' (CEC) system is an [[engine management system]] designed and used by [[American Motors|American Motors Corporation]] (AMC) and [[Jeep]] on 4- and 6-cylinder engines of its own manufacture from 1980 to 1990.<ref>{{cite book|url= https://books.google.com/books?id=UOA5O0tMLXoC&q=AMC+also+has+used+a+computerized+emission+control+(CEC)+system+on+4-+and+6-+cylinder+engines+of+its+own+manufacture+since+1980 |page=308 |title=Automotive electrical and electronic systems, Volume 2 |series=Harper & Row/Chek-Chart automotive series |first=Roger |last=Fennema |publisher=HarperCollins |year=1987 |isbn=9780064540148 |via=Google Books |accessdate=28 May 2022}}</ref> It is one of the three major components for proper engine operation: the computer, electrically controlled carburetor, and the oxygen sensor in the exhaust system.<ref>{{cite web |title=The Three Major Players |url= http://gleebledorf.com/major.html |website=gleebledorf.com |access-date=28 May 2022}}</ref>

Starting with the 1986 model year, the [[AMC straight-4 engine]]s used a throttle body injection (TBI) or [[Fuel injection#Single-point injection|single-point]], fuel injection system with a new fully computerized engine control.<ref>{{cite journal|url= https://books.google.com/books?id=duMDAAAAMBAJ&dq=AMC+Computerized+Engine+Control&pg=PA35 |page=35 |title=Detroit '86: Technical Highlights |journal=Popular Mechanics |date=October 1985 |volume=162 |issue=10 |via=Google Books |accessdate=28 May 2022}}</ref> In addition to cycling the fuel injector (pulse-width time, on–off), the engine control computer also determined the ignition timing, idle speed, [[exhaust gas recirculation]], etc.<ref>{{cite book|title=Automotive Computers and Digital Instrumentation |page=283 |first=Robert N. |last=Brady |publisher=Prentice Hall |year=1988 |isbn=9780835902632}}</ref>

==Operation==
The AMC Computerized Engine Control is an electronic fuel feedback system is similar to those used by other automakers at the time by controlling the amount of gasoline to be atomized by the carburetor by precise electronic calculations.<ref name="vcfed">{{cite web |title=Depotting an 80's MCU from Ford...for AMC |url= https://forum.vcfed.org/index.php?threads/depotting-an-80s-mcu-from-ford-for-amc.1070440/ |publisher=Vintage Computer Federation Forums |date=27 May 2019 |access-date=28 May 2022}}</ref> The AMC CEC was unique in that almost all of its sensors and actuators were [[Digital data|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 [[pneumatic motor|motor]] for the other) to control idle speed.<ref>{{cite web|url= https://4wdmechanix.com/moses-ludels-4wd-mechanix-magazine-rebuilding-the-yj-wrangler-4-2l-bbd-carburetor/ |title=How-to: YJ Wrangler 4.2L Six Two-Barrel 'BBD' Carburetor Rebuild! |date=22 April 2015 |first=Moses |last=Ludel |publisher=4WD Mechanix Magazine |accessdate=28 May 2022}}</ref> The CEC also controlled ignition timing using information from the fuel-control section and an [[Engine knocking|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 [[Duraspark]] [[ignition system]]. Although built by Ford, the CEC module is not related to the [[Ford EEC]] systems internally.

The AMC CEC went through at least four revisions.<ref name="vcfed"/>
* The first included a "Check Engine" light.
* The second included new process cycles with electric timing retard and the added "Pulse-Air" injection system for emissions control.
* The third version was updated in 1983 to a new style called the C4 system which used a new microcontroller. The 1983 model year, the {{convert|258|CID|L|1|abbr=on}} I6 engine featured the MCU-Super D electronics, "Pulse-Air", and an increased compression ratio, from 8.6:1 to 9.2:1.<ref>{{cite book|url= https://archive.org/details/jeepcolorhistory00stev |url-access= registration |quote= AMC MCU Super-D. |page= [https://archive.org/details/jeepcolorhistory00stev/page/105 105] |title=Jeep Color History |first=Steve |last=Statham |publisher=MBI Publishers |year=1999 |isbn=9780760306369}}</ref>
* The fourth version followed shortly.

==Maintenance==
The system uses a maze of emissions vacuum hoses.<ref name="EFIoptions">{{cite web|url= http://www.geekthing.com/~robf/jeep/tech/efi.html |title=EFI Options for the AMC 6-258 Engine |first=Mark |last=Shipman |website=geekthing.com |accessdate=28 May 2022}}</ref> Because of the many vacuum-driven components and electrical connections in the system, CEC-equipped engines have developed a reputation of being hard to tune.<ref>{{cite web|url= http://www.offroaders.com/tech/jeep/engine-factory-amc258i6.htm |title=AMC 258 I6 |website=offroaders.com |accessdate=28 May 2022}}</ref> American Motors issued a Technical Service Bulletin to diagnose low or inconsistent [[engine idle]] speeds on 1980 through 1988 [[AMC Eagle]] automobile.<ref>{{cite web |url= http://wiki.amcevolution.com/index.php/Correctly_setting_your_idle_speed_1980_-_1988 |title=AMC Technical Service Bulletin 12E460 – The idle speed may be too low or inconsistent on your 1980 – 1988 Eagle automobile |publisher=AMC Evolution |date=4 February 2013 |archive-url= https://web.archive.org/web/20140313194927/http://wiki.amcevolution.com/index.php/Correctly_setting_your_idle_speed_1980_-_1988 |archive-date=13 March 2014 |url-status=dead |access-date=28 May 2022}}</ref>

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 a rough idle and stalling. In places where emissions testing is not required, a modification is by bypassing the computer and disabling the BBD's Idle Servo, or replacing the BBD with a manually tuned carburetor. Several vendors (including [[Chrysler]] and [[Edelbrock]]) offer retrofit kits that replace the CEC and the carburetor with fuel injection.<ref name="EFIoptions"/>

==References==
{{reflist}}

==External links==
* {{cite web |title=Jeep Adventures Under the Hood |url= http://gleebledorf.com/ |website=gleebledorf.com |date=3 August 2020 |access-date=28 May 2022}}, a guide to the CEC system and how to tune it.
* {{cite web |title=The "Nutter" Bypass |url= http://www.4x4wire.com/jeep/tech/electrical/jn-ignition99/ |website=4x4wire.com |date=2019 |access-date=28 May 2022}}

{{American Motors}}

[[Category:Engine control systems]]
[[Category:AMC engines|Computerized Engine Control]]
[[Category:American Motors|Computerized Emission Control]]
[[Category:Engine technology]]
[[Category:Engines]]
[[Category:Automotive technology tradenames]]

AMC computerized engine control - Revision history

imported>Citation bot: Altered url. URLs might have been anonymized. | Use this bot. Report bugs. | Suggested by Feetsicle | Category:Engine technology | #UCB_Category 56/206