1987 MAZDA 626 fuel

4B DECELERATION CONTROL SYSTEM
DECELERATION CONTROL SYSTEM
This system consists of the dashpot and fuel cut system. The dashpot is to prevent after-burn so that
the throttle valve gradually closes during deceleration.
The control unit detects engine deceleration judging from the engine speed and the idle switch, and
signals a fuel cut operation to match the engines need, based on the coolant temperature and the
driving condition.
4B—64

DECELERATION CONTROL SYSTEM 4B
COMPONENT DESCRIPTIONS
Component Function Remarks
Brake light switch Detects braking operation (deceleration);
sends signal to engine control unit
Clutch switch Detects in-gear condition;
sends signal to engine control unit Switch ON when clutch pedal released
Dashpot (MTX) Prevents sudden closing of throttle valve during deceleration or shifting Adjustment speed: 1,900—2,100 rpm
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 Installed in throttle sensor
Ignition coil (-) terminal Detects engine speed; sends signal to engine control unit
Neutral switch Detects in-gear condition; sends signal to engine control unit Switch ON when in-gear
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)
76G04B-089
4B—65

4B DECELERATION CONTROL SYSTEM
TROUBLESHOOTING
Check the condition of the wiring harness and connectors before checking the sensor or switches below.
Note
Make the system inspection first. If no problem is found, continue with the next system
inspection of the Troubleshooting Guide. (Refer to page 4B—7 and 8.)
Possible
^^ cause
Symptom
Dashpot Water thermo
sensor
Electrical signal
inspection
(Injector)
Possible
^^ cause
Symptom 4B—67 4B—97 4B-66
High idle speed after warming up 1
Runs rough on deceleration 1 3 2
Afterburn in exhaust system 1 3 2
Poor fuel consumption 1 3 2
Fails emission test 1 3 2
76G04B-090
Electrical Signal Inspection (Injector)
1. Connect the SST between the wiring harness and
engine control unit.
2. Set 3C or 3E position on the SST.
Note
3C — For No. 2 and No. 4 injectors
3E — For No. 1 and No. 3 injectors
76G04B-091
0-6V 0-20V
3. Check that the indicator lamps alternately flash at
idle.
86U04A-125
4B—66

4B EEC SYSTEM
EVAPORATIVE EMISSION CONTROL
(EEC)
SYSTEM
Engine control unit
Solenoid valve
(Purge control)
Vacuum
switch
valve x
From water thermo valve To dynamic -chamber
Three-way
check valve
Orifice Charcoal
canister
From fuel tank
No.2 purge
control valve
Fuel tank
86U04A-136
This system stores fuel vapor generated in the fuel tank in the canister when the engine is not running.
The fuel vapor is stored in the canister until it is drawn into the dynamic chamber and burned when
the engine is started.
COMPONENT DESCRIPTIONS
Component Function Remarks
Air flow meter Detects amount of intake air; sends signal to engine control unit
Intake air thermo sensor and fuel pump
switch are integrated
Charcoal canister Stores fuel tank fumes when engine
stopped
Engine control unit Detects signals from input sensors and switches; controls solenoid valve (Purge control)
Ignition coil (-)
terminal Detects engine speed; sends signal to
engine control unit
Separator Prevents fuel from flowing into charcoal canister
Solenoid valve (Purge control) Controls vacuum line to vacuum switch valve
Three-way check valve Controls pressure in fuel tank
Vacuum switch valve Regulates evaporative fumes from canis-
ter to intake manifold
Water thermo sensor Detects coolant temperature; sends signal to engine control unit
Water thermo valve Controls vacuum applied to No.1 purge control valve and solenoid valve (Purge control)
Opens vacuum line above 54°C (129°F)
76G04B-104
4B—74

CONTROL SYSTEM 4B
CONTROL SYSTEM
Atmospheric
pressue sensor
Engine control unit
Brake light switch
Clutch switch
Circuti opening
relay
E/L control unit
Air flow meter
Neutral switch
76G04B-129
The control system consists of the input devices and the engine control unit. The engine control unit
controls the fuel injection amount (EGI), fuel injection pressure, bypass air amount, switch monitor func-
tion, and fail-safe function.
4B—83

4B CONTROL SYSTEM
RELATIONSHIP CHART
Input Devices and Output Devices
BRAKE LIGHT SWITCH O X X X X X X X X X
ELECTRICAL LOAD CONTROL UNIT X X X X X X X X O X
P/S PRESSURE SWITCH* X X X X X X X X O X
A/C SWITCH O X X X X O O X X O
IGNITION SWITCH
(STA

POSITION) O O X O X X X X O O
INHIBITOR SWITCH o X X X O X X X X O
NEUTRAL
AND
CLUTCH SWITCH o X X X X X X X X O
OXYGEN SENSOR o X X X X X X X X X
WATER THERMO SWITCH (RADIATOR) o X X X O X X X X X
ATMOSPHERIC PRESSURE SENSOR o X X X X O X O O X
INTAKE
AIR
THERMO SENSOR o X X O X X X O O X
WATER THERMO SENSOR o X X O O O X X o X
IDLE SWITCH o o X O X X X X o X
THROTTLE SENSOR o O X X O X X X X O
AIR FLOW METER o X X X X O X X X X
IGNITION COIL o O X O O O X X o O

INPUT
DEVICES
OUTPUT
DEVICES
FUEL
INJECTION
AMOUNT FUEL
INJECTION

TIMING
PRESSURE
REGULATOR
EGR
PURGE
IDLE-UP
(A)*
IDLE-UP
(B)

IDLE-UP

(C)

rr

INPUT
DEVICES
OUTPUT
DEVICES
INJECTOR
AIR

VALVE
SOLENOID
VALVE
AIR

BYPASS
SOLENOID
VALVE
AIR

CONDITIONEI

76G04B-108
4B-84

4B CONTROL SYSTEM
AIR FLOW METER
Potentiometer
Intake air thermo
sensor Fc EI E2 VB VC VS THA
Fuel pump switch
Connector-—
I
lOQDOQOD i
69G04C-100
Inspection
1. Remove the air flow meter. (Refer to page 4B—31)
2. Check the air flow meter body for cracks.
3. Verify that the measuring plate moves smoothly.
4. Disconnect the connector from the air flow meter.
5. Using an ohmmeter, check resistance between the
terminals with the measuring plate fully closed and
fully open.
6. Connect the connector to the air flow meter after
inspecting.
76G04B-112
Terminal Resistance (Q) Terminal Fully closed | Fully open
E2<->VS More than 20
E2«VC 100-300
E2«VB 200-400
E2«THA (Intake air thermo sensor)
-20°C (—4°F) 13.6-18.4 kfi 20°C (68°F) 2.21-2.69 kfi 60°C (140°F) 493—667 0
Ei<->Fc OO 0
Note
Refer to page 4B—31 for replacement of the
air flow meter.
76G04B-113
4B—94

4C
FUEL AND EMISSION
CONTROL SYSTEMS
(FUEL INJECTION FE DOHC)
OUTLINE 4C— 2
COMPONENT APPLICATION 4C— 2
SYSTEM DIAGRAM 4C— 3
COMPONENT LOCATION 4C— 4
VACUUM HOSE ROUTING
DIAGRAM 4C— 7
SPECIFICATIONS 4C— 8
TROUBLESHOOTING GUIDE 4C— 9
TROUBLESHOOTING WITH SST.. 4C— 11
INSPECTION PROCEDURE 4C— 12
PRINCIPLE OF CODE CYCLE 4C— 13
CODE NUMBER 4C— 14
SWITCH MONITOR FUNCTION 4C— 25
INSPECTION PROCEDURE 4C— 26
IDLE ADJUSTMENT 4C— 29
IDLE SPEED 4C— 29
IDLE MIXTURE 4C— 30
INTAKE AIR SYSTEM 4C— 31
COMPONENT DESCRIPTION 4C— 31
REMOVAL 4C— 32
PARTS INSPECTION 4C— 33
REPLACEMENT 4C— 36
INSTALLATION 4C— 37
VARIABLE INERTIA CONTROL
(VIC) SYSTEM 4C— 39
COMPONENT DESCRIPTION 4C— 40
TROUBLESHOOTING 4C— 40
IDLE SPEED CONTROL
(ISC) SYSTEM 4C— 44
COMPONENT DESCRIPTION 4C— 45
TROUBLESHOOTING 4C— 46
REMOVAL 4C— 48
FUEL SYSTEM 4C— 49
COMPONENT DESCRIPTION 4C— 50
TROUBLESHOOTING 4C— 51
FUEL PRESSURE RELEASE AND
SERVICING FUEL SYSTEM 4C— 52
MULTI-PRESSURE TESTER 4C— 53
FUEL PUMP 4C— 56
PULSATION DAMPER 4C— 57
INJECTOR 4C— 57
TRANSFER PUMP CONTROL
SYSTEM 4C— 59
REPLACEMENT 4C— 60
FUEL TANK 4C— 65
PRESSURE REGULATOR
CONTROL (PRC) SYSTEM 4C— 68
COMPONENT DESCRIPTION 4C— 69
TROUBLESHOOTING 4C— 69
DECELERATION CONTROL
SYSTEM 4C— 72
COMPONENT DESCRIPTION 4C— 73
TROUBLESHOOTING 4C— 73
ELECTRONIC SPARK ADVANCE
(ESA) CONTROL SYSTEM 4C— 75
COMPONENT DESCRIPTION 4C— 76
TROUBLESHOOTING 4C— 76
EXHAUST GAS RECIRCULATION
(EGR) SYSTEM 4C- 77
COMPONENT DESCRIPTION 4C— 77
TROUBLESHOOTING 4C— 78
EVAPORATIVE EMISSION
CONTROL (EEC) SYSTEM 4C— 80
COMPONENT DESCRIPTION 4C— 80
TROUBLESHOOTING 4C— 81
POSITIVE CRANKCASE
VENTILATION (PCV) SYSTEM.... 4C— 86
COMPONENT DESCRIPTION 4C— 86
PCV VALVE 4C— 86
EXHAUST SYSTEM
(UNLEADED FUEL) 4C— 87
REMOVAL AND INSTALLATION.. 4C— 88
INSPECTION 4C— 88
EXHAUST SYSTEM
(LEADED FUEL) 4C— 89
REMOVAL AND INSTALLATION.. 4C— 90
CONTROL SYSTEM 4C— 91
RELATIONSHIP CHART 4C— 92
EGI MAIN FUSE 4C— 96
CONTROL RELAY 4C— 96
NEUTRAL SWITCH 4C— 97
CLUTCH SWITCH 4C— 97
P/S PRESSURE SWITCH 4C— 97
ENGINE CONTROL UNIT 4C— 98
E/L CONTROL UNIT 4C—102
AIR FLOW SENSOR 4C—103
THROTTLE SENSOR 4C—104
IDLE SWITCH 4C—106
WATER THERMO SWITCH 4C—106
WATER THERMO SENSOR 4C—107
OXYGEN SENSOR 4C—107
DISTRIBUTOR 4C—108
OXYGEN SENSOR HEATER 4C—109
KNOCK SENSOR 4C—109
INTAKE AIR THERMO SENSOR .. 4C—110
76G04C-001