Feedback Carburetor System Mazda 626 GC

DESCRIPTION

The Mazda 626 models use a computerized engine control system to reduce exhaust emissions and maintain good fuel economy.

The main function of the system is the control of the EGR control valve and air/fuel ratio under all operating conditions. All system functions are governed by an electronic control unit located behind the right kick panel in the passenger compartment.

CONTROL UNIT

Through various sensors, the control unit detects the following: Engine speed, intake manifold vacuum, coolant temperature, oxygen concentration in exhaust system, EGR control valve position, throttle opening, in-gear position and air conditioner ON/OFF condition.

The control unit governs the operation of the feedback-type carburetor, EGR system, and air injection system.

AIR/FUEL SOLENOID VALVES

The air/fuel solenoid valve is located in the carburetor. It controls the air/fuel ratio depending on engine speed, temperature, and load condition. It operates according to a signal from the control unit.

AIR CONDITIONING SOLENOID VALVE

The 3-way solenoid valve is part of the idle up system. It controls the vacuum to the servo diaphragm through a signal from the control unit when the AC switch is closed.

AIR CONTROL VALVES

The air control valves are part of the air injection system. They help govern the flow of secondary air to the reed valves in the air cleaner.

The No. 1 air control valve controls the flow of secondary air to reed valve "A" according to intake manifold vacuum. If also supplies air when 3-way solenoid valve is "ON".

The No. 2 air control valve (Federal models only) is used in conjunction with the No. 1 valve to control air flow to reed valve "A". No. 2 air control valve is vacuum actuated. The vacuum signal is controlled by the ACV solenoid valve which in turn is governed by the control unit.

ALTITUDE COMPENSATOR

Federal vehicles are equipped with an altitude compensator which maintains the air/fuel mixture in the intake manifold. It adds air to carburetor air bleeds when atmospheric pressure drops due to elevation. On GLC models, the altitude compensator also helps govern the operation of the EGR valve.

COASTING RICHER SOLENOID VALVE

The coasting richer solenoid valve is located in the carburetor secondary fuel circuit. If functions after 1 second when engine speed is 1400-2000 and the idle, neutral, and clutch switch are off.

CLUTCH & NEUTRAL SWITCH

The clutch and neutral switches detect in-gear condition. The neutral switch is closed in neutral and open in all other ranges. The clutch switch is on when the clutch pedal is depressed and off when pedal is released.

DUTY SOLENOID VALVES

The duty solenoid valves consist of the vent and vacuum valves. Their purpose is to control vacuum to the EGR valve. The duty solenoid valves are controlled by signals from the control unit.

The vent valve is connected to the air cleaner and controls fresh air flow to the duty solenoid valve. The vacuum valve controls intake manifold vacuum flow.

EGR Control Valve

The EGR valve supplies exhaust gas to the intake manifold. It operates during acceleration and constant speed driving. The EGR valve is vacuum actuated. The vacuum signal is governed by the control unit.

EGR Position Sensor

The EGR position sensor detects the lift of the EGR valve and sends the signal to the control unit.

IDLE UP SYSTEM

The idle up system increases engine RPM at idle on models equipped with air conditioning and/or power steering. Engine idle is increased through use of a servo diaphragm.

IDLE SWITCH

The idle switch, located on the carburetor, detects throttle opening for the control unit. The idle switch is off at idle and on at 1200-1300 RPM in neutral.

OXYGEN SENSOR

The oxygen sensor is part of a closed loop system which consists of the control unit and the sensor. The sensor detects the exhaust manifold oxygen concentration and sends the signal to the control unit.

POWER STEERING SOLENOID VALVE

The power steering solenoid valve is part of the idle-up system. The solenoid valve controls the vacuum signal to the servo diaphragm thereby increasing idle speed. The solenoid valve is actuated by the power steering switch.

POWER STEERING SWITCH

The power steering switch is activated by power steering fluid pressures above 355 psi (25 kg/cm 2 ). When activated, the switch provides a ground for the power steering solenoid valve.

SERVO DIAPHRAGM

The servo diaphragm opens the throttle valve by the negative pressure from the 3-way solenoid valve during A/C and power steering operation.

The servo is also activated during power steering operation when pressures rise to a predetermined level.

On manual transaxles, the servo operates when the engine speed is 900 RPM. On automatic transaxles, the servo operates when the engine speed is 1150 RPM.

SLOW CUT FUEL SOLENOID VALVE

The slow fuel cut solenoid valve closes the carburetor primary slow port fuel line during deceleration and when the ignition switch is off. The valve will function at 2000 RPM or higher if idle, neutral, and clutch are off.

VACUUM SENSOR

Detects intake manifold vacuum and sends the signal to the control unit.

VACUUM SWITCH

The vacuum switch is part of a system to improve driveability while driving at high altitudes.

When the vacuum of the intake manifold nears atmospheric pressure, the vacuum switch will turn off and send a signal to the control unit. The control unit will send a signal to the air/fuel solenoid in the carburetor to supply additional fuel.

WATER THERMO SENSORS & SWITCHES

Water thermo sensors detect the intake manifold coolant temperature for the control unit. They are located in the intake manifold coolant passage. Water thermo switches detect radiator coolant temperature and send the signal to the control unit.

Emission Control Component Location. Scheme 19

TESTING & ADJUSTMENT

Note. Testing of the Air/Fuel Solenoid Valve will be found in the appropriate article in FUEL SYSTEMS Section.

AIR/FUEL SOLENOID VALVE

Testing of air/fuel solenoid valve requires carburetor disassembly. See appropriate carburetor article in FUEL SYSTEMS Section.

At altitudes of 3609 ft. (1100 m) or above, the altitude compensator passages should be blocked. The air passages should be open at lower elevations. (Scheme 20)

Altitude Compensator Systems. Scheme 20

System Check

1. Warm engine to operating temperature and run at idle. Turn air conditioner on and check that servo diaphragm stem is raised.
2. The servo diaphragm is activated when the air conditioner is on and engine speed is 1300 RPM.
3. Turn air conditioner off. Turn steering wheel all the way to the right or left and ensure servo diaphragm stem is raised. If system does not respond as described, check the 3-way solenoid valves, servo diaphragm and control unit signal.

3-Way Solenoid Valves

1. Unplug connector from air conditioning solenoid valve. Ground the Black/Red terminal and apply 12V to Black/White terminal. With power applied, the solenoid valve should be open.
2. Unplug connector from power steering solenoid valve. Ground the Green/Red terminal and apply 12V to Black/White terminal. Solenoid valve should be open. (Scheme 21)

Idle Up System 3-Way Solenoid Valves. Scheme 21

1. Start engine and run at idle. Unplug the power steering switch connector from the steering gear housing. Turn the steering wheel all the way to the left or right. Ensure there is continuity between the switch terminals.
2. When the oil pressure is above 355 psi (25 kg/cm 2 ), the switch should be on. At pressures below 355 psi (25 kg/cm 2 ), the switch should be off.

Scheme 22

1. Remove the air cleaner. Plug the hoses of the idle compensator, thermo sensor and the reed valves. Warm up engine to operating temperature. All accessories should be off. Do not adjust while the electric fan motor is running.
2. On models with air conditioner only, disconnect the A/C solenoid valve-to-servo vacuum sensing tube from the servo diaphragm. Apply manifold vacuum to the servo diaphragm. Engine speed should increase to 1200-1400 RPM. If not, turn adjusting screw. (Scheme 22) (Scheme 22): Adjusting Servo Diaphgarm (A/C Models)
3. If a vehicle is equipped with A/C and power steering, follow procedures outlined in step 1) before continuing. On power steering models, disconnect the power steering solenoid valve-to-servo vacuum sensing tube.
4. Apply manifold vacuum to the servo. Engine speed should increase to 800-1000 RPM on manual transaxle models and 1050-1250 RPM on automatic transaxle models.
5. If engine speed must be adjusted, turn the adjusting screw on the servo diaphragm head. Recheck engine speed.

Idle Up System. Scheme 23

Scheme 24

1. Run the engine at idle. Connect a voltmeter to the vacuum switch connector Green terminal. Voltmeter should read below 1.5V. Disconnect and plug vacuum sensing tube from the vacuum switch. Voltmeter should read 12V. (Scheme 24) (Scheme 24): Testing Vacuum Switch
2. The vacuum switch may be tested off the vehicle. Connect a vacuum pump and a circuit tester to the switch. At atmospheric pressure, there should be no continuity between the switch terminals. Switch should show continuity at 2.36 in. Hg or below.

WATER THERMO SWITCHES

1. Remove switch from lower left hand corner of radiator. On GLC models, the switch will have Green/Red and Black wires attached to it. Green/Black and Black wires are attached to the switch.
2. Place the switch in water with a thermometer and heat up water gradually. Check the temperature at which continuity exists between both terminals of the switch.
3. The switch should show continuity at 59.4-66.6°F (15-19°C). Replace the switch if it does not agree with standard value.

WATER THERMO SENSOR

Remove water thermo sensor from the intake manifold. Sensor will have Blue/Red and Blue/Yellow wires attached. Place sensor in water with a thermometer and heat up water gradually. Check calibration of the sensor. See WATER THERMO SENSOR CALIBRATION table.

WATER THERMO SENSOR CALIBRATION

CONTROL UNITS

1. The control unit may be tested with a voltmeter. Engine must be at operating temperature. For testing, ignition switch must be "ON" and engine not running. Measure voltage at each terminal and compare values to appropriate Control Unit Testing chart.
2. The control unit has a built-in fail safe mechanism. If certain malfunctions occur during driving, the control unit will automatically initiate a command so driving performance will not be affected. See «CONTROL UNIT MALFUNCTION CHART»(/mazda/626/gc-1982-1987/remont/testing-diagnostics/#feedback-carburetor-system) .

CONTROL UNIT MALFUNCTION CHART

CONTROL UNIT TESTING - KEY ON, NORMAL OPERATING TEMPERATURE

Computerized Engine Control Wiring Diagram. Scheme 25

See also:
• WATER THERMO SENSOR CALIBRATION