The GM designed Computer Controlled Catalytic Converter System (C-4), was introduced in 1979 and used on 4-151 engines through 1980.  The C-4 System primarily maintains the ideal air/fuel ratio at which the catalytic converter is most effective.

Some versions of the system also control ignition timing of the distrubutor.

The Computer Command Control System (CCC system), introduced on some 1980 California models and used on all 1981 and later carbureted car lines, is an expansion of the C-4 system.  The CCC system monitors up to 15 engine/vehicle operating conditions which uses to control up to nine engine and emissions control systems.  In addition to maintaining the ideal air/fuel ratio for the catalytic converter and adjusting ignition timing, the CCC system also controls the air management system so that the catalytic converter can operate at the highest efficiency possible.  The system also controls the lockup on the transmission torque converter clutch (certain automatic transmission models only), adjust idle speed over a wide range of conditions, purges the evaporative emissions charcoal canister, controls the EGR valve operation and operates the Early Fuel Evaporative (EFE) system.  Not all engines use all of the above systems.

There are two operation modes for both the C-4 System and the CCC system: closed loop and open loop fuel control.  Closed loop fuel control means that the oxygen sensor is controlling the carburetor's air/fuel mixture ratio.  Under open loop fuel control operating conditions (wide open throttle, engine and/or oxygen sensor cold), the oxygen has no effect on the air/fuel mixture.

Major components of the system include an Electronic Control Module (ECM), an oxygen sensor, and electronically controlled variable mixture carburetor, and a three-way oxidation/reduction catalytic converter.

The oxygen sensor generates a voltage which varies with exhaust gas oxygen content.  Lean mixtures (more oxygen) reduce voltage, rich mixtures (less oxygen) increase voltage.  Voltage output is sent to the ECM.

An engine temperature sensor installed in the engine coolant outlet monitors coolant temperatures.  Vacuum control switches and throttle position sensors also monitor engine conditions and supply signals to the ECM.

The Electronic Control Module (ECM) monitors the voltage input of the oxygen sensor along with information from other input signals.  It processes these signals and generates a control signal sent to the carburetor.  The control signal cycles between ON (lean command) and OFF (rich command).  The amount of ON and OFF time is a function of the input voltage sent to the ECM by the oxygen sensor.  The ECM has a calibration unit called a Programmable Read Only Memory (PROM) which contains the specific instructions for a given engine application.  In other words, the PROM assembly is a replaceable component which plugs into a socket on the ECM and requires a special tool for removal and installation.

To maintain good idle and drivability under all conditions, other input signals are used to modify the ECM output signal.  Besides the sensors and switches already mentioned, these input signals include the Manifold Absolute Pressure (MAP) or vacuum sensors and the Barometric Pressure (BARO) sensor.  The MAP or vacuum sensors sense changes in manifold vacuum, while the BARO sensor senses changes in barometric pressure.  One important function of the BARO sensor is the maintenance of good engine performance at various altitudes.  These sensors act as throttle position sensors on some engines.  See the following paragraph for a description.

A Rochester Dualjet carburetor is used with the C-4 system.  It may be an E2SE, E2SME, E4MC or E4ME model, depending on engine application.  An electronically operated mixture control solenoid is installed in the carburetor float bowl.  The solenoid controls the air/fuel mixture metered to the idle and main metering systems.  Air metering to the idle system is controlled by an idle air bleed valve.  It follows the movement of the mixture solenoid to control the amount of air bled into the idle system, enriching of leaning out the mixture as appropriate.  Air/fuel mixture enrichment occurs when the fuel valve is open and the air bleed is closed.  All cycling of this system, which occurs ten times per second, is controlled by the ECM.  A throttle position switch informs the ECM of open or closed throttle operation.  A number of different switches are used, varying with application.  The 4-cylinder engine (151 cu. in.) uses two vacuum switches to sense wide open throttle and closed throttle operation.

The Computer Command Control (CCC) has many components in common with the C-4 system (although they should probably not be interchanged between systems).  These include the Electronic Control Module (ECM), which is capable of monitoring and adjusting more sensors and components than the ECM used on the C-4 system, an oxygen sensor, an electronically controlled variable mixture carburetor, a three-way catalytic converter, throttle position and coolant sensors, a Barometric Pressure (BARO) Sensor, a Manifold Absolute Pressure (MAP) sensor, a "check engine" light on the instrument cluster, and an Electronic Spark Control (ESC) which retards ignition spark under some conditions (detonation, etc.)

Components used almost exclusively by the CCC System include the Air Injection Reaction (AIR) management system, charcoal canister purge solenoid, EGR valve control, Vehicle Speed Sensor (VSS) located in the instrument cluster, transmission torque converter clutch solenoid (automatic transmission models only), idle speed control, and early fuel evaporate (EFE) system.

See the operation descriptions under the C-4 system for those components (except ECM) the CCC system shares with the C-4 system.

The CCC system ECM, in addition to monitoring sensors and sending a control signal to the carburetor, also control the following components of sub systems: charcoal canister purge, AIR management system, idle speed control, automatic transmission converter lockup, distributor ignition timing, EGR valve control, EFE control, and the air conditioner compressor clutch operation.  The CCC EMC is equipped with a PROM assembly similar to the one used in the C-4 ECM.  See above description.

The AIR management system is an emission control which provides additional oxygen either to the catalyst of the cylinder head ports (in some cases exhaust manifold).  An AIR management system, composed of an air switching valve and/or an air control valve, controls the air pump flow and is itself controlled by the ECM.  A complete description of the AIR system is given elsewhere in this unit repair section.  The major difference between the CCC AIR system and the systems used on other cars is that the flow of air from the air pump is controlled electrically by the ECM. rather than the vacuum signal.

The charcoal canister purge control is an electrically operated solenoid valve controlled by the ECM.  When energized, the purge control solenoid blocks vacuum from reaching the canister purge valve.  When the ECM de-energized the purge control solenoid, vacuum is allowed to reach the canister and operate the purge valve.  This releases the fuel vapors collected in the canister into the induction system.

The EGR valve control solenoid is activated by the ECM in similar fashion to the canister purge solenoid.  When the engine is cold, the ECM energized the solenoid, which blocks the vacuum signal to the EGR valve.  When the engine is warm, the ECM de-energized the solenoid and the vacuum signal is allowed to reach and activate the EGR valve.

The Transmission Converter Clutch (TCC) lock is controlled by the ECM through an electrical solenoid in the automatic transmission.  When the vehicle speed sensor in the instrument panel signals the ECM that the vehicle has reached the correct speed, the ECM energizes the solenoid  which allows the torque converter to mechanically couple the engine to the transmission.  When the brake pedal is pushed or during deceleration, passing, etc., the ECM returns the transmission to fluid drive.

The Early Fuel Evaporative (EFE) system is used on some engines to provide rapid heat to the engine induction system to promote smooth start-up and operation.  There are two types of system: vacuum servo and electrically heated.  They use different means to achieve the same end, which is to pre-heat the incoming air/fuel mixture.  They are controlled by the ECM.

American Motors introduced feedback systems on all cars (except Eagle) in 1980.  Two different, but similar systems are used.  The four cylinder engine used the G.M. C-4 feedback system, which is covered earlier in this section.  Component usage is identical to that of the 4-151 engine, including oxygen sensor, a vacuum switch (which is closed at idle and partial trottle positions), a wide open throttle switch, a coolant temperature sensor (set to open at 150F [66C]), and Electronic Control Module (ECM) equipped with PROM, and a mixture control solenoid installed in the air horn on the E2SE carburetor.  A 'Check Engine' light is included on the instrument panel as a service and diagnostic indicator.

The 6-cylinder engine is equipped with a Computerized Emission Control (CEC) System.

In 1980 CEC components include an oxygen sensor; two vacuum switches (on ported and one manifold) to detect three operating conditions; idle, part throttle, and wide open throttle; a coolant temperature switch; a Micro Computer Unit (MCU), the control unit for the system which monitors all data and sends an output signal to the carburetor; and a stepper motor installed in the main body of the BBD carburetor, which varies the position of the two metering pins controlling the size of the air bleed orifices in the carburetor.  The MCU also interrupts signals from the distributor (rpm voltage) to monitor engine rpm.

On 1981 and later models with CEC, the number of sensors has been increased.  Three vacuum operated electric switches, two mechanically operated switches, one engine coolant switch and an air temperature operated switch are used to detach and send operating data to the MCU concerning the following engine operating conditions: cold engine start-up and operation; wide open throttle; idle (closed throttle); and partial and deep throttle.

Both AMC systems are conventional in operation.  As in other feedback systems, two modes of operation are possible; open loop and closed loop.  Open loop operation occurs during engine starting, cold engine operation, cold oxygen sensor operation, engine idling, wide open throttle operation, and low battery voltage operation.  In open loop, a fixed air/fuel mixture signal is provided by the ECM or MCU to the carburetor, and oxygen sensor data is ignored.  Closed loop operation occurs at all other times, and in this mode all signals are used by the control unit to determine the optimum air/fuel mixture.

Before suspecting the C-4 or CCC System or any of its components as faulty, check the ignition system including distributor, timing, spark plugs and wires.  Check the engine compression, air cleaner, and emission control components not controlled by the ECM.  Also check the intake manifold, vacuum hoses and hose connectors for leaks and the carburetor for tightness.

The following systems could indicate a possible problem with the C-4 or CCC System.

1. Detonation
2. Stalls or rough idle, cold
3. Stalls or rough idle, hot
4. MIssing
5. Hesitation
6. Surges
7. Poor gasoline mileage
8. Sluggish or spongy
9. Hard starting, cold
10. Hard starting, hot
11. Objectionable exhaust odors
12. Cuts out

As a bulb check, the 'Check Engine' light will come on when the ignition switch is turned to the ON position but the engine is not started.  The 'Check Engine' light will also produce the trouble code or codes by a series of flashes which translate as follows.  When the diagnostic test lead (C-4) or terminal (CCC) under the dash is grounded, with the ignition in the ON position and the engine not running, the 'Check Engine' light will flash once, pause, then flash twice in rapid succession.  This is a code 12, which indicates that the diagnostic system is working.  After a longer pause, the code 12 will repeat itself two more times.  The cycle will then repeat itself until the engine is started or the ignition of turned OFF.

When the engine is started, the 'Check Engine' light will remain on for a few seconds, then turn OFF.  If the 'Check Engine' light remains on, the self-diagnostic system has detected a problem.  If the test lead (C-4) or test terminal (CCC) is then grounded, the trouble code will flash three times.  If more than one problem is found, each trouble code will flash three times.  Trouble codes will flash in numerical order (lowest code number to highest).  The trouble code series will repeat as long as the test lead or terminal is grounded.

A trouble code indicates a problem with a given circuit.  For example, trouble code 14 indicated a problem in the cooling sensor circuit.  This includes the coolant sensor, its electrical harness, and the Electronic Control Module (ECM).

Since the self-diagnostic system cannot diagnose every possible fault in the system, the absence of a trouble code does not mean the system is trouble free.  To determine problems within the system which do not activate a trouble code, a system performance check must be made.  This job should be left to a qualified technician.

In case of an intermittent fault in the system, the 'Check Engine' light will go out when the fault goes away, but the trouble code will remain in the memory of the ECM.  Therefore, if a trouble code can be obtained even though the 'Check Engine' light is not on, the trouble code must be evaluated.  If must be determined if the fault is intermittent or if the engine must be at certain operating conditions (under load, etc.) before the 'Check Engine' light will come on.  Some trouble codes will not be recorded in the ECM until the engine had been operated at part throttle for about 5 to 18 minutes.

On the C-4 system, the ECM erases all trouble codes every time the ignition is turned OFF.  In the case of intermittent faults, a long term memory is desirable.  This can be produced by connecting the orange connector/lead from terminal 'S' of the ECM directly to the battery (or to a 'hot' fuse panel terminal).  This terminal must be disconnected after diagnosis is complete or it will drain the battery.

On the CCC system, a trouble code will be stored until terminal 'R' of the ECM has been disconnected from the battery for 10 seconds.

An easy way to erase the computer memory on the CCC system is to disconnect the battery terminals from the battery.  If this method is used, don't forget to reset clocks and electronic preprogramable radios.  Another method is to remove the fuse marked ECM in the fuse panel.  Not all models have such a fuse.

On the C-4 system, activate the trouble code by grounding the trouble code test lead.  Use the illustration to locate the test lead under the instrument panel (usually a white and black wire or a wire with a green connector).  Run a jumper wire from the lead to ground.

On the CCC system, locate the test terminal under the instrument panel.  Ground the test lead.  On many systems, the test lead is situated side by side with a ground terminal.  In addition, on some models, the partition between the test terminal and the ground terminal has a cut out section so that a spade terminal can be used to connect the two terminals.