GM Celebrity/Century/Ciera/6000 1982-1996 Repair Guide

Feedback Carburetor and Computer Command Control (CCC) System

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The CCC system monitors engine and vehicle operating conditions which it uses to control engine and emission control systems. This system controls engine operation and lowers the exhaust emissions while maintaining good fuel economy and driveability. The Computer Control Module (ECM/PCM) is the brain of the CCC system. The ECM/PCM controls engine related systems constantly adjusting the engine operation. 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 lock-up on the transaxle's torque converter clutch, adjusts 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 subsystems.

The CCC system is primarily an emission control system, designed to maintain a 14.7:1 air/fuel ratio under all operating conditions. When this ideal air/fuel ratio is maintained the catalytic converter can control oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) emissions.

There are 2 operation modes for CCC system: closed loop and open loop fuel control. Closed loop fuel control means 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 sensor has no effect on the air/fuel mixture.

On some engines, the oxygen sensor will cool off while the engine is idling, putting the system into open loop operation. To restore closed loop operation, run the engine at part throttle and accelerate from idle to part throttle a few times.

The basic system block diagram shows the catalytic converter located in the exhaust system close to the engine. It is ahead of the muffler and tailpipe. If the converter is to do its job effectively, the engine must receive an air/fuel mixture of approximately 14.7:1.

The carburetor mixes air and gasoline into a combustible mixture before delivering it to the engine. However, carburetors have reached a point where they can no longer control the air/fuel mixture sufficiently close to the ideal 14.7:1 ratio for most operating conditions. Therefore, a different type of control must be used on the carburetor, something that has never been used before.

An electric solenoid in the carburetor controls the air/fuel ratio. The solenoid is connected to an electronic module (ECM/PCM) which is an on board computer. The ECM/PCM provides a controlling signal to the solenoid. The solenoid controls the metering rod(s) and an idle air bleed valve to closely control the air/fuel ration throughout the operating range of the engine. However, since the engine operates under a wide variety of conditions, the computer must be told what those conditions are. This is so that it will know what to tell the carburetor solenoid to do.

A sensor is located in the exhaust stream close to the engine. It's known as an oxygen sensor or usually refer to as the O 2 S sensor. This sensor functions when the engine's exhaust temperature rises above 600°F (315°C). There is a direct relationship between the mixture delivered by the carburetor and the amount of oxygen left in the exhaust gases. The O 2 S sensor can determine whether the exhaust is too rich or too lean. It sends a varying voltage signal to the ECM/PCM.

The ECM/PCM will then signal the mixture control solenoid to deliver richer or leaner mixture for the current engine operating conditions. As the carburetor makes a change, the O 2 S sensor will sense that change and signal the ECM/PCM whether or not it's too rich or too lean. The ECM/PCM will then make a correction, if necessary. This goes on continually and is what we refer to as Closed Loop operation. Closed loop conditions deliver a 14.7:1 air/fuel mixture to the engine. This makes it possible for the converter to act upon all 3 of the major pollutants in an efficient and effective manner. consider, however, what happens in the morning when it's cold and the vehicle is started. If the system where to keep the air/fuel mixture to the 14.7:1 air/fuel ratio when it's cold the chances are that the engine wouldn't run very well. When the engine is cold, it has to have a richer mixture. An automatic choke is used to give the engine a richer mixture until it is up to normal operating temperature. during this time, the O 2 S sensor signals are ignored by the ECM/PCM.

A temperature sensor is located in the water jacket of the engine and connected to the electronic control module. When the engine is cold, the temperature sensor will tell the ECM/PCM to ignore the oxygen sensor signal, since the sensor is too cold to operate. The electronic control module then tells the carburetor to deliver a richer mixture based upon what has already been programmed into the ECM/PCM. The ECM/PCM will also use information from other sensors during cold start operation.

After the engine has been running for some time and has reached normal operating temperature, the temperature sensor will signal the ECM/PCM that the engine is warm and it can accept the oxygen sensor signal. If other system requirements are met, closed loop operations begins. The oxygen sensor will then influence the ECM/PCM as to what mixture it should deliver to the engine. In addition to these 2 conditions, there are 3 other conditions which affect the air/fuel mixture delivered to the engine. First is the load that is placed upon the engine. When an engine is working hard, such as pulling a heavy load up a long grade, it requires a richer air/fuel mixture. This is different from a vehicle that is operating in a cruise condition on a level highway at a constant rate of speed.

Manifold vacuum is used to determine engine load. A manifold pressure sensor is connected to the intake manifold. It detects changes in the manifold pressure which are signalled to the ECM/PCM. As changes occur, the load placed upon the engine varies. The ECM/PCM takes this varying signal into account when determining what mixture the carburetor should be delivering to the engine. The next condition in determining what air/fuel mixture should be is the amount of throttle opening. The more throttle opening at any given time, the richer the mixture required by the engine. On most applications a Throttle Position Sensor (TPS) in the carburetor sends a signal to the ECM/PCM. It tells the ECM/PCM the position of the throttle, whether it is at idle, part or wide-open throttle.

The last condition, which has a bearing on the mixture that the engine would require, is the speed the engine is running. Certainly when an engine is operating at 600 rpm, it doesn't need as much gasoline as it does when it is operating at 4000 rpm. Therefore, a tachometer signal from the distributor is delivered to the ECM/PCM. This tells the ECM/PCM how fast the engine is running. This signal will also be taken into consideration when the ECM/PCM decides what mixture the carburetor should be delivering to the engine. In the typical CCC system, the ECM/PCM will use various inputs to make decisions that will best control the operation of the mixture control solenoid for maximum system efficiency.

CCC SYSTEM COMPONENTS



Computer Control Module

The Electronic Control Module (ECM) and the Powertrain Control Module (PCM) are one and the same. While older vehicles have the ECM name badge and newer vehicles the PCM, they are both computer control modules. The ECM/PCM is a reliable solid state computer, protected in a metal box. It is used to monitor and control all the functions of the CCC system and is located in on the passenger side kick panel. The ECM/PCM can perform several on-car functions at the same time and has the ability to diagnose itself as well as other CCC system circuits.

The ECM/PCM performs the functions of an on and off switch. It can send a voltage signal to a circuit or connect a circuit to ground at a precise time. Programmed into the ECM/PCM's memory are voltage and time values. These valves will differ from engine to engine. As an example then, if the ECM/PCM sees a proper voltage value for the correct length of time it will perform a certain function. This could be turning the EGR system on as the engine warms up. If however, the voltage or the time interval is not correct, the ECM/PCM will also recognize this. It will not perform its function and in most cases turn the "CHECK ENGINE" or "SERVICE ENGINE SOON" light on.

The other CCC components include the oxygen sensor, an electronically controlled variable-mixture carburetor, a 3-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 Timing (EST) distributor, which on some engines is equipped with an Electronic Spark Control (ESC) or Knock Sensor (KS), which retards ignition spark under some conditions (detonation, etc.).

Other components used by the CCC system include the Air Injection Reaction (AIR) Management System, charcoal canister purge solenoid, EGR valve control, vehicle speed sensor (located in the instrument cluster), transaxle torque converter clutch solenoid (automatic transaxle models only), idle speed control and Early Fuel Evaporative (EFE) system.

The CCC system ECM/PCM, in addition to monitoring sensors and sending a control signal to the carburetor, also controls the charcoal canister purge, AIR Management System, fuel control, idle speed control, idle air control, automatic transaxle converter clutch lock-up, distributor ignition timing, EGR valve control, EFE control, air conditioner compressor clutch operation, electric fuel pump and the "CHECK ENGINE" light.

The AIR Management System is an emission control which provides additional oxygen either to the catalyst or the 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/PCM. The AIR system uses vacuum operated, ECM/PCM controlled (grounds to complete the circuit and energize the solenoids) valves to control the AIR switching.

The charcoal canister purge control is an electrically operated solenoid valve controlled by the ECM/PCM. When energized, the purge control solenoid blocks vacuum from reaching the canister purge valve. When the ECM/PCM de-energizes 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/PCM in similar fashion to the canister purge solenoid. When the engine is cold, the ECM/PCM energizes the solenoid, which blocks the vacuum signal to the EGR valve. When the engine is warm, the ECM/PCM de-energizes the solenoid and the vacuum signal is allowed to reach and activate the EGR valve.

The Torque Converter Clutch (TCC) lock-up is controlled by the ECM/PCM through an electrical solenoid in the automatic transaxle. When the vehicle speed sensor in the instrument panel signals the ECM/PCM that the vehicle has reached the correct speed, the ECM/PCM 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/PCM returns the transaxle to fluid drive.

The idle speed control adjusts the idle speed to load conditions and will lower the idle speed under no-load or low-load conditions to conserve gasoline.

The Early Fuel Evaporative (EFE) system is used on most engines to provide rapid heat to the engine induction system to promote smooth start-up and operation. There are 2 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 may or may not be controlled by the ECM/PCM.

A/C Wide Open Throttle (WOT) Control: on this system the ECM/PCM controls the A/C compressor clutch to disengage the clutch during hard acceleration. On some engines, the ECM/PCM disengages the clutch during the engine start-up on a warm engine. The WOT control is not installed on all engines.

Electronic Spark Control (ESC) or Knock Sensor (KS): on this system the ECM/PCM controls spark timing on certain engines to allow the engine to have maximum spark advance without spark knock. This improves the driveability and fuel economy. This system is not used on all engines.

Shift Light Control, as equipped on some vehicles, utilizes an ECM/PCM activated light to indicate the best manual transaxle shift point for maximum fuel economy. This control is not used on all engines.

Rochester Feedback Carburetors

The E2ME and E2MC are 2-barrel single stage design. All carburetors are used with the Computer Command Control (CCC) System of fuel control. All Rochester carburetors consist of 3 major assemblies: the air horn, the float bowl and the throttle body. They have 6 basic operating systems: float, idle, main metering, power, pump and choke.

A single float chamber supplies fuel to the carburetor bores. A closed-cell rubber float, brass needle seat and a rubber tipped float valve with pull clip, are used to control fuel level in the float chamber. An electrically operated mixture control solenoid, mounted in the float bowl, is used to control the air and fuel mixture in the primary bores of the carburetor. The plunger in the solenoid is controlled (or pulsed) by electrical signals received from the Computer Control Module (ECM/PCM).

The air valve and metering rods control the air/fuel metering in the secondary bores. A pair of tapered metering rods are attached to a hanger, which operates by cam action resulting from the air valve angle and provides the additional fuel flow necessary during increased engine air flow at wide open throttle.

General Motors Rochester carburetors are identified by their model code. The carburetor model identification number is stamped vertically on the float bowl, near the secondary throttle lever. The letters in the model name describe the specific features of the carburetor. For example: The first letter "E" indicates the carburetor is Electronically controlled. The second and third digits, "2S" indicates the carburetor is a member of the Varajet family. The last digit "E" indicates an integral Electric choke. The identification code is stamped on the float bowl.

If a carburetor number has an "E" at the end (such as E2ME), that carburetor has an integral Electric Choke.

For Carburetor repair, overhaul or adjustment, refer to procedures covered in Fuel System (Fuel Systems).

DIAGNOSIS & TESTING



The following explains how to activate the trouble code signal light in the instrument cluster and gives an explanation of what each code means. This is not a full CCC system troubleshooting and isolation procedure.

Before suspecting the 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/PCM. Also check the intake manifold, vacuum hoses and hose connectors for leaks and the carburetor bolts for tightness.

The following symptoms could indicate a possible problem with the CCC system.



Detonation
 
Stalls or idles rough when cold
 
Stalls or idles rough when hot
 
Missing
 
Hesitation
 
Surges
 
Poor gasoline mileage
 
Sluggish or spongy performance
 
Hard starting - cold
 
Objectionable exhaust odors (rotten egg smell)
 
Cuts out
 
Improper idle speed
 

As a bulb and system 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 terminal 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 long pause, the code 12 will repeat itself 2 more times. The cycle will then repeat itself until the engine is STARTED or the ignition is 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 terminal is then grounded, the trouble code will flash 3 times. If more than a single problem is found, each trouble code will flash 3 times. Trouble codes will flash in numerical order (lowest code number to highest). The trouble codes series will repeat as long as the test terminal is grounded.

A trouble code indicates a problem with a given circuit. For example, trouble code 14 indicates 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.

In the 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, it a trouble code can be obtained even though the "CHECK ENGINE" light is not on, the trouble code must be evaluated. It 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/PCM until the engine has been operated at part throttle for about 5-18 minutes. On the CCC system, a trouble code will be stored until terminal R of the ECM/PCM 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 preprogrammable radios. Another method is to remove the fuse marked ECM/PCM in the fuse panel. Not all models have such a fuse.

CCC System Circuit Diagnosis

To diagnose CCC system circuits, use the same general troubleshooting approach that is used for other automotive electrical systems. Finding the fault in a CCC circuit will require the testing tools described in this section. These tools are used with the diagnostic charts for CCC system troubleshooting. Always use a digital voltmeter for accuracy of readings when using CCC diagnostic charts.

Testing CCC System Performance

A dwellmeter is used to analyze operation of the M/C solenoid circuit. The operation of that circuit is controlled by the ECM/PCM, which used information from the sensors.

A chart called the "System Performance Check" is provided in the section. This chart provides step-by-step instructions to determine if the M/C control solenoid circuit, ECM/PCM and various sensors (M/C control system) are functioning properly. If they are not, the chart indicates the steps to take in order to locate and repair the source of the trouble.

Charts for the other systems, such as AIR, EST, EGR, EFE, TCC and canister purge are also provided in the section. Another chart called the "Diagnostic Circuit Check" follows the system performance check. This chart is the starting point for any diagnosis.

The dwellmeter is used to diagnose the M/C control system. Connect a dwellmeter to the pigtail connector in the M/C solenoid wiring harness. In the old contact point style ignition system, the dwellmeter read the period of time that the points were closed (dwell) and voltage flowed to the ignition coil.

In the CCC system the dwellmeter is used to read the time that the ECM/PCM closed the M/C solenoid circuit to ground, allowing voltage to operate the M/C solenoid. Dwell, as used in CCC system performance diagnosis, is the time that the M/C solenoid circuit is closed (or energized). The dwellmeter will translate this time into degrees. The 6-cylinder (0-60 degree) scale on the dwellmeter is used for this reading. The ability of the dwellmeter to perform this kind of conversion makes it an ideal tool to check the amount of time the ECM/PCM,'s internal switch is closed, thus energizing the M/C solenoid. The only difference is that the degree scale on the meter is more like the percent of solenoid ON time rather than actual degrees of dwell.

Connecting the Dwellmeter

First set the dwellmeter on the 6-cylinder position, then connect it to the Mixture Control (M/C) solenoid dwell lead to measure the output of the ECM/PCM. Do not allow the terminal to touch ground, including any hoses. The dwellmeter must be set to the 6-cylinder position when diagnosing all engines, whether working on a 4, 6, or 8-cylinder engine.

Some older dwellmeters may not work properly on CCC. Don't use any dwellmeter which causes a change in engine operation when it is connected to the solenoid lead.

The 6-cylinder scale on the dwellmeter provides evenly divided points, for example:



15 degrees = 1 / 4 scale
 
30 degrees = midscale
 
45 degrees = 3 / 4 scale
 

Connect the positive clip lead of the dwellmeter to the M/C solenoid pigtail connector shown in. Attach the other dwellmeter clip lead to ground. Do not allow the clip leads to contact other conductive cables or hoses which could interfere with accurate readings.

After connecting the dwellmeter to a warm, operating engine, the dwell at idle and part throttle will vary between 5-55 degrees. That is, the needle will move continuously up and down the scale. Needle movement indicates that the engine is in closed loop and that the dwell is being varied by signals from the ECM/PCM. However, if the engine is cold, has just been restarted, or the throttle is wide open, the dwell will be fixed and the needle will be steady. Those are signs that the engine is in open loop.

Diagnostic checks to find a condition without a trouble code are usually made on a warm engine (in closed loop) as indicated by a hot upper radiator hose. There are 3 ways of distinguishing open from closed loop operation.

  1. A variation in dwell will occur only in closed loop.
  2.  
  3. Test for closed loop operation. Cause the mixture to become richer, by restricting the air flow through into the carburetor or manually closing the choke. If the dwellmeter moves up scale, that indicates closed loop.
  4.  
  5. If a large vacuum leak is created and the dwell drops down, that also indicates closed loop.
  6.  

Reading the Dwellmeter

The mixture control (M/C) solenoid moves the metering rods up and down 10 times per second. This frequency was chosen to be slow enough to allow full stop-to-stop M/C solenoid travel, but fast enough to prevent any undesirable influence on vehicle response.

The duration of the on period determines whether the mixture is rich (mostly up) or lean (mostly down). When the metering rods are down for a longer period (54 degrees) than they are up (6 degrees), a lean mixture results.

As the solenoid on-time changes, the up time and down time of the metering rods also changes. When a lean mixture is desired, the M/C solenoid will restrict fuel flow through the metering jet 90% of the time, or, in other words, a lean mixture will be provided to the engine.

This lean command will read as 54 degrees on the dwellmeter (54 degrees is 90% of 60 degrees). This means the M/C solenoid has restricted fuel flow 90% of the time. A rich mixture is provided when the M/C solenoid restricts fuel flow only 10% of the time and allows a rich mixture to flow to the engine. A rich command will have a dwellmeter reading of 6 degrees (10% of 60 degrees); the M/C solenoid has restricted fuel flow 10% of the time.

On some engines dwellmeter readings can vary between 5-55 degrees, rather than between 6-54 degrees. The ideal mixture would be shown on the dwellmeter with the needle varying or swinging back and forth, anywhere between 10-50 degrees. Varying means the needle continually moves up and down the scale. The amount it moves does not matter, only the fact that it does move. The dwell is being varied by the signal sent to the ECM by the oxygen sensor in the exhaust manifold.

Under certain operating conditions such as Wide Open Throttle (WOT), or a cold engine, the dwell will remain fixed and the needle will be steady. Remember, a low dwellmeter reading (5-10°) announces the ECM signal to the M/C control solenoid is a rich command, while 55° would indicate a lean command.

Open and Closed Loop Operation

Two terms are often used when referring to CCC system operation. They are closed loop and open loop.

Basically, closed loop indicates that the ECM/PCM is using information from the exhaust oxygen sensor to influence operation of the mixture control (M/C) solenoid. the ECM/PCM still considers other information, such as engine temperature, rpm, barometric and manifold pressure and throttle position, along with the exhaust oxygen sensor information.

During open loop, all information except the exhaust oxygen sensor input is considered by the ECM/PCM to control the M/C solenoid. The diagnostic charts are based on a warmed up engine (closed loop operation) and will generally state, run engine at part throttle for 3 minutes or until there is a varying dwellmeter indication before beginning diagnosis.

It is important to note that the exhaust oxygen sensor may cool below its operational temperature during prolonged idling. This will cause an open loop condition and make the diagnostic chart information not usable during diagnosis. Engine rpm must be increased to warm the exhaust oxygen sensor and re-establish closed loop. Diagnosis should begin again at the first step on the chart after closed loop is resumed.

DIAGNOSTIC PROCEDURES



Following is a complete diagnostic sequence for the CCC system. In all cases, the sequence is begun with routine engine checks. After performing a system diagnostic circuit check, use the code chart (if applicable) or other diagnostic chart. Conduct a system performance check after testing and service are completed.

Diagnostic Charts

This section contains tree-type charts for locating the source of a fault in the CCC system circuits. When using a tree chart, always start at the first step and follow the sequence from top to bottom. Often there will be several branches of the tree to follow. Follow the branch that is applicable to the result obtained in that step. Several charts will be used during diagnosis and this sequential approach should be used in all cases.

The CCC system should not be considered as a possible source of poor engine performance, fuel economy, or excessive emissions until all the routine engine checks, such as ignition, spark plugs, air cleaner and vacuum hoses, have been made.

SYSTEM DIAGNOSTIC CIRCUIT CHECK



Begin the Diagnostic Circuit Check by making sure that the diagnostic system itself is working. Turn the ignition to ON with the engine stopped. If the "CHECK ENGINE" or "SERVICE ENGINE SOON" light comes on, ground the diagnostic code terminal (test lead) under the dash. If the "CHECK ENGINE" or "SERVICE ENGINE SOON" light flashes Code 12, the self-diagnostic system is working and can detect a faulty circuit. If there is no Code 12, see the appropriate chart in this section. If any additional codes flash, record them for later use.

If a Code 51 flashes, use chart 51 to diagnose that condition before proceeding with the Diagnostic Circuit Check. A Code 51 means that the "CHECK ENGINE" or "SERVICE ENGINE SOON" light flashes 5 times, pauses, then flashes once. After a longer pause, code 51 will flash again twice in this same way. To find out what diagnostic step to follow, look up the chart for Code 51 in this section. If there is not a Code 51, follow the "No Code 51" branch of the chart.

Clear the ECM memory by disconnecting the voltage lead either at the fuse panel or the ECM letter connector for 10 seconds. This clears any codes remaining from previous repairs, or codes for troubles not present at this time. Remember, even though a code is stored, if the trouble is not present the diagnostic charts cannot be used. The charts are designed only to locate present faults.

When erasing the computer memory on the CCC system the ignition switch must be turned OFF before removing any fuses, wire connectors or battery cables. If the battery cable is to disconnect from the battery, don't forget to reset clocks and electronic preprogrammable radios.

Next, remove the TEST terminal ground, set the parking brake and put the transaxle in P . Run the warm engine for several minutes, making sure it is run at the specified curb idle. Then, if the "CHECK ENGINE" or "SERVICE ENGINE SOON" light comes on while the engine is idling, ground the TEST lead again and observe (count) the flashing trouble code.

If the "CHECK ENGINE" or "SERVICE ENGINE SOON" light does not come on, check the codes which were recorded earlier. If there were no additional codes, road test the vehicle for the problem being diagnosed to make sure it still exists.

The purpose of the Diagnostic Circuit check is to make sure the "CHECK ENGINE" or "SERVICE SOON SOON" light works, that the ECM is operating and can recognize a fault and to determine if any trouble codes are stored in the ECM memory.

If trouble codes are stored, it also checks to see if they indicate an intermittent problem. This is the starting point of any diagnosis. If there are no codes stored, move on to the System Performance Check.

The codes obtained from the "CHECK ENGINE" or "SERVICE ENGINE SOON" light display method indicate which diagnostic charts provide in the section are to be used. For example, code 23 can be diagnosed by following the step-by-step procedures on chart 23.

If more than a single code is stored in the ECM/PCM, the lowest code number must be diagnosed first. then proceed to the next highest code. The only exception is when a 50 series flashes. 50 series code take precedence over all other trouble codes and must be dealt with first, since they point to a fault in the PROM unit or the ECM/PCM.

SERVICE



Before suspecting the CCC system, or any of its components as being faulty, check the ignition system (distributor, timing, spark plugs and wires). Check the engine compression, the air cleaner and any of the emission control components that are not controlled by the ECM/PCM. Also check the intake manifold, the vacuum hoses and hose connectors for any leaks. Check the carburetor mounting bolts for tightness.

The following symptoms could indicate a possible problem area with the CCC system:



Detonation
 
Stalling or rough idling when the engine is cold
 
Stalling or rough idling when the engine is hot
 
Missing
 
Hesitation
 
Surging
 
Poor gasoline mileage
 
Sluggish or spongy performance
 
Hard starting when engine is cold
 
Hard starting when the engine is hot
 
Objectionable exhaust odors
 
Engine cuts out
 
Improper idle speed
 

As a bulb and system 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/codes by a series of flashes which translate as follows: When the diagnostic test terminal under the instrument panel is grounded, with the ignition in the ON position and the engine not running, the Check Engine light will flash once, pause, and then flash twice in rapid succession. This is a Code 12, which indicates that the diagnostic system is working. After a long pause, the Code 12 will repeat itself two more times. This whole cycle will then repeat itself until the engine is started or the ignition switch is turned OFF.

When the engine is started, the Check Engine light will remain on for a few seconds and then turn off. If the Check Engine light remains on, the self-diagnostic system has detected a problem. If the test terminal is then grounded, the trouble code will flash (3) three times. If more than one problem is found to be in existence, each trouble code will flash (3) three times and then change to the next one. Trouble codes will flash in numerical order (lowest code number to highest). The trouble code series will repeat themselves for as long as the test terminal remains grounded.

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

Since the self-diagnostic system cannot diagnose every possible fault in the system, the absence of a trouble code does not necessarily mean that the system is trouble-free. To determine whether or not a problem with the system exists that does not activate a trouble code, a system performance check must be made. You can follow the symptom charts for the fuel system your car has. If the chart doesn't help you find the problem or instructs you to more involved testing using special tool you may wish to seek a qualified service technician. Guessing which component to test or testing a component incorrectly can be very expensive.

In the 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/PCM. Therefore, if a trouble code can be obtained even though the Check Engine light is not on, it must still be evaluated. It must be determined if the fault is intermittent or if the engine must be operating under certain conditions (acceleration, deceleration, etc.) before the Check Engine light will come on. In some cases, certain trouble codes will not be recorded in the ECM/PCM until the engine has been operated at part throttle for at least 5 to 18 minutes.

On the CCC system, a trouble code will be stored until the terminal R at the ECM/PCM has been disconnected from the battery for at least 10 seconds, or the battery cable has be removed.

ACTIVATING THE TROUBLE CODE



On the CCC system, locate the test terminal under the instrument panel. Use a jumper wire and ground only the lead.

Ground the test terminal according to the instructions given previously in the Basic Troubleshooting section.

CARBURETOR COMPONENT TESTING



Electric Choke

Check the choke unloader and idle setting adjustments. The choke linkage and fast idle cam must operate freely. Bent, dirty or otherwise damaged linkage must be cleaned, repaired or replaced as necessary. Do not lubricate linkage since lubricant will collect dust and cause sticking.

  1. Allow the choke to cool so that when the throttle is opened slightly, the choke blade fully closes.
  2.  
  3. Start the engine and determine the time for the choke blade to reach the full open position.
  4.  
  5. If the choke blade fails to open fully within 3 1 / 2 minutes, proceed with Step 4 and 5 below.
  6.  
  7. Check the voltage at the choke heater connection (engine must be running):
    1. If the voltage is approximately 12-15 volts, replace the electric choke unit.
    2.  
    3. If the voltage is low or zero, check all wires and connections. If any connections in the oil pressure switch circuitry are faulty, or if pressure switch is failed open, the oil warning light will be on with the engine running. Repair wires or connectors as required.
    4.  

  8.  
  9. If Steps 4a and 4b do not correct the problem, replace oil pressure switch. No gasket is used between the choke cover and the choke housing due to grounding requirements.
  10.  

Hot Air Choke
  1. With the parking brake applied and the drive wheels blocked, place the transaxle in P or N , start the engine and allow it to warm up. Visually check to be sure the choke valve fully opens.
  2.  
  3. If the choke fails to open fully, momentarily touch the choke housing and the hot air inlet pipe or hose, to determine if sufficient heat is reaching the choke stat.
  4.  


CAUTION
The choke housing and hot air inlet pipe or hose will be HOT to the touch; use caution to prevent burns.

  1. If the choke housing and or heat inlet are cool to the touch, check for a loss of vacuum to the housing, restricted heat inlet pipe in the choke housing or choke heat pipe, or restricted passages in the manifold choke heat stove.
  2.  
  3. Replace or correct as necessary.
  4.  

Float Level

This is an external check procedure.

  1. Remove the air horn vent stack.
  2.  
  3. With engine idling and choke wide open, insert gauge J-9789-135, or equivalent, in vent slot or vent hole. Allow the gauge to float freely.
  4.  
  5. Observe the mark on the gauge that lines up with the top of the casting.
  6.  
  7. Setting should be within 1 / 16 in. (2mm) of the specified float level setting.
  8.  
  9. If not within specified range, check fuel pressure.
  10.  
  11. If fuel pressure is correct, remove air horn and adjust float.
  12.  

Mixture Control Solenoid

This is a mixture control solenoid travel test. Before checking the mixture control solenoid travel, it may be necessary to modify the float gauge J-9789-130 or equivalent (used to externally check the float level).

This should be done by filing or grinding the sufficient material off the gauge to allow for insertion down the vertical D-shaped hole in the air horn casting (located next to the idle air bleed valve cover).

Check that the gauge freely enters the D-shaped vent hole and does not bind. The gauge will also be used to determine the total mixture control solenoid travel.

With the engine off and the air cleaner removed, measure the control solenoid travel as follows:

  1. Remove the air horn vent stack.
  2.  
  3. Insert a modified float gauge J-9789-130 or equivalent down the D-shaped vent hole. Press down on the gauge and release it.
  4.  
  5. Observe that the gauge moves freely and does not bind. With the gauge released (solenoid in the up position), be sure to read it at eye level and record the mark on the gauge that lines up with the top of the air horn casting (upper edge).
  6.  
  7. Lightly press down on the gauge until bottomed (solenoid in the down position). Record the mark on the gauge that lines up with the top of the air horn casting.
  8.  
  9. Subtract the gauge up dimension from gauge dimension. Record the difference. This difference is total solenoid travel.
  10.  
  11. If total solenoid travel is not 1 / 16 - 1 / 8 in. (2-3mm), perform the mixture control solenoid adjustments. If the difference is 1 / 16 - 1 / 8 in. (2-3mm), proceed to the idle air bleed valve adjustment.
  12.  

If adjustment is required, it will be necessary to remove the air horn and drive out the mixture control solenoid screw plug from the under side of the air horn.

Idle Load Compensator (ILC)
  1. Inspect the condition of the tube cap covering the access to plunger travel adjustment screw. If missing or damaged, the diaphragm chamber will lose vacuum.
  2.  
  3. Hold throttle lever half open, to allow ILC to extend fully.
  4.  
  5. Apply finger pressure to the ILC plunger.
  6.  
  7. Apply 20 in. Hg (68 kPa) of vacuum to the ILC, plunger should begin to retract. If not replace the ILC.
  8.  
  9. Observe vacuum gauge, vacuum should hold for at least 20 seconds, if not replace the ILC.
  10.  
  11. Release vacuum from the ILC. The plunger should extend, if not replace the ILC.
  12.  

 
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