1987 MAZDA 626 Workshop Manual

4C DECELERATION CONTROL SYSTEM
DECELERATION CONTROL SYSTEM
Distributor
(Ne signal)
Idle switch
QSO-Water thermo sensor
=5
A/C switch
Engine control unit
Detection of
fuel cut
condition Determi-
nation of
fuel cut
speed
* *
1
T
No.3

I
No.4
No.2
The fuel cut system is provided as a deceleration control system.
This system is to improve fuel consumption.
86U04A-121
4C—72

DECELERATION CONTROL SYSTEM 4C
COMPONENT DESCRIPTION
Component Function Remarks
Engine control unit Detects signals from input sensors and switches; cuts fuel injection
Idle switch Detects when throttle valve fully closed; sends signal to engine control unit ON at idle
Ne signal pick-up Detects crank angle at 180° intervals; sends signal to engine control unit Installed in distributor
Water thermo sensor Detects coolant temperature; sends signal to engine control unit
76G04C-135
TROUBLESHOOTING
Check the condition of the wiring harness and connectors before checking the sensor or switches.
Note
Make the system inspection first. If no problem is found, continue with inspection of the
next system of the Troubleshooting Guide. (Refer to page 4C—10 and 11.)
Possible cause Water thermo sensor System inspection
Page 4C—107 4C—74
Checking order 2 1
76G04C-136
4C-73

4C DECELERATION CONTROL SYSTEM
System Inspection (Electrical Signal)
1. Connect the SST between the wiring harness and
control unit.
2. Set 3C, 3E 3F, or 3H position on the SST.
Note
3C — For No. 2 injector
3E — For No. 1 injector
3F — For No. 4 injector
3H — For No. 3 injector
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3. Check that the indicator lamps alternately flash at
idle.
86U04A-125
0-6V 0-20V
® $
4. Increase the engine speed to 4,000 rpm, then sud-
denly decrease the engine speed.
5. Check that the green indicator lamp is OFF dur-
ing deceleration.
6. Accelerate and check that the voltage decreases.
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4C—74

ESA CONTROL SYSTEM 4C
ELECTRONIC SPARK ADVANCE
(ESA)
CONTROL SYSTEM
Throttle sensor
76G04C-139
This system electronically controls the ignition timing to obtain better engine performance.
The best ignition timing is determined and set within the engine control unit based on signals from
the various sensors and switches.
The knock control function is used only with leaded fuel engines.
4C-75

4C ESA CONTROL SYSTEM
COMPONENT DESCRIPTION
Component Function Remark
Air flow sensor Detects amount of intake air;
sends signal to engine control unit
Distributor Has Ne and G signal pick-up and distributes high voltage to spark plugs
Engine control unit Detects signals from input sensors and switches; decides best ignition timing
Idle switch Detects when throttle valve fully closed; sends signal to engine control unit Installed on throttle body
Igniter Receives spark signal from engine control unit and generates high voltage in ignition coil
Ignition switch
(ST position) Sends engine cranking signal to engine con-trol unit
Ne signal pick-up Detects crank angle at 180° intervals; sends signal to engine control unit Installed in distributor
Knock sensor (leaded fuel) Detects engine knocking; sends signal to knock control unit
Throttle sensor Detects throttle opening angle; sends signal to engine control unit Installed on throttle body
76G04C-140
TROUBLESHOOTING
Check the condition of the wiring harness and connectors before checking the sensors or switches.
Note
If no problem is found, continue with inspection of the next system of the troubleshooting
Guide. (Refer to page 4C—10 and 11)
Possible cause
Page
Symptom
Air flow sensor Igniter Engine control
unit terminal Knock sensor Possible cause
Page
Symptom
Air flow sensor Igniter
1X
Knock sensor Possible cause
Page
Symptom
4C—103 Refer to section 5 4C—98 4C—109
Hard start or won't start (Cranks OK) 3 1 2 —
Knocking — 1
76G04C-141
4C-76

EGR SYSTEM (UNLEADED FUEL) 4C
EXHAUST GAS RECIRCULATION
(EGR)
SYSTEM (UNLEADED FUEL)
This system introduces exhaust gas into the intake manifold to reduce NOx emissions. It operates de-
pending on the engine load, engine speed (1,500—3,500 rpm), engine coolant temperature (above
70°C, 158°F), and radiator coolant temperature (above 17°C, 63°F).
COMPONENT DESCRIPTION
Component Function Remark
EGR control valve Recirculates portion of exhaust gas
EGR modulator valve Controls vacuum acting on EGR control valve
Engine control unit Detects signals from input sensors and switches; con-trols solenoid valve (EGR)
Ne signal pick-up Detects crank angle at 180° intervals; sends signal to engine control unit
Solenoid valve (EGR) Controls vacuum to EGR control valve
Throttle sensor Detects throttle valve opening angle; sends signal to en-
gine control unit
Installed on throttle body
Water thermo sensor Detects coolant temperature; sends signal to engine control unit
Water thermo switch Detects radiator coolant temperature; sends signal to engine control unit ON: above 17°C (63°F)
76G04C-143
AC—17

4C EGR SYSTEM (UNLEADED FUEL)
TROUBLESHOOTING
Check the condition of the wiring harness and connectors before checking the sensors or switches.
Note
Make the system inspection first. If no problem is found, continue with inspection of the
next system of the Troubleshooting Guide. (Refer to pages 4C—10 and 11.)
Possible cause
Throttle
sensor
Solenoid valve
(EGR)
EGR
modula-
tor valve
EGR con-trol valve
Water
thermo
sensor
Water
thermo switch
Engine control unit
terminal
System in-spection
2N
Page 4C—104 4C—78 4C—79 4C—79 4C—107 4C—106 4C—98 4C—78
Checking order 8 2 4 3 6 5 7 1
76G04C-144
System Inspection
1. Start the engine.
2. Accelerate the engine while still cold and verify that
the diaphragm of the EGR control valve does not
move.
3. Warm up the engine to normal operating temper-
ature and run it at idle.
Warning
Be careful when checking the EGR control
valve, the surrounding area is very hot.
4. Accelerate the engine and check that the di-
aphragm of the EGR control valve moves.
Solenoid Valve (EGR)
1. Disconnect the vacuum hose from the vacuum
pipe.
2. Blow through the solenoid valve from vacuum hose
A.
3. Check that air flows from port B.
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4C-78

EGR SYSTEM (UNLEADED FUEL) 4C
Apply 12V
J* Port
76G04C-147
86U04A-133
76G04C-148
4. Disconnect the solenoid valve connector.
5. Connect 12V and a ground to the terminals of the
solenoid valve.
6. Blow through the solenoid valve from vacuum hose
A.
7. Check that air flows from the air filter.
EGR Modulator Valve
1. Remove the EGR modulator valve.
2. Plug the No. 1 port and connect a vacuum pump
to the No. 3 port.
3. Blow into the exhaust gas port. Operate the vacu-
um pump and verify that vacuum is held.
4. Release the exhaust gas port and confirm that
vacuum is released.
EGR Control Valve
1. Warm up the engine and run at idle.
2. Disconnect the vacuum hose from the EGR con-
trol valve and plug it.
3. Verify that the engine runs smoothly.
4. If not correct, clean the exhaust gas passage in
the valve or replace the valve.
Note
Before replacing the EGR control valve, check
the intake air and control systems.
5. Connect a vacuum pump to the valve and apply
vacuum.
6. Verify that the engine runs roughly or stalls at more
than the specified vacuum.
Specification:
40—60 mmHg (1.6—2.4 inHg)
7. If not correct, replace the EGR control valve.
76G04C-149
4C-79