engine MAZDA 626 1987 Workshop Manual

4C ISC SYSTEM

IDLE
SPEED CONTROL
(ISC)
SYSTEM
Air valve BAC valve (ISC valve + air valve)
ISC valve
Air passage
c=£> Coolant passage
Idle switch
Large
Bypass air
amount
Small
Characteristics of air valve
Low 50°C (122°F) High
Coolant temperature
76G04C-077
To improve idle smoothness, the ISC system controls the intake air amount by regulating the bypass
air amount that passes through the throttle body.
This system consists of the BAC valve and the control system.
The BAC valve consists of the air valve which functions only when the engine is cold (below 50°C
(122°F)) and the ISC valve which works throughout the entire engine speed range.
4C-44

ISC SYSTEM 4C
COMPONENT DESCRIPTION
Component Function Remark
A/C switch Detects air conditioner operation; sends
signal to engine control unit Switch ON when air conditioner
operating
Air valve When cold, supplies bypass air into dy-namic chamber • Engine speed increased to shorten warm-up period • Thermo wax type
• Installed in BAC valve
Clutch switch Detects in-gear condition; sends signal to engine control unit Switch ON when clutch pedal released
E/L control unit Detects that E/L is being applied; sends
signal to engine control unit
Engine control unit Detects signals from input sensors and switches; controls solenoid valve (Idle speed control)
Idle switch Detects when throttle valve fully closed;
sends signal to engine control unit
Installed on throttle body
Ne signal pick-up Detects crank angle at 180° intervals; sends signal to engine control unit Installed in distributor
Neutral switch Detects in-gear condition; sends signal to engine control unit
Switch ON when in gear
P/S pressure switch Detects P/S operation; sends signal to engine control unit Switch ON when steering wheel turned right or left
Solenoid valve (Idle speed control) Controls bypass air amount • Controlled by duty signal from engine control unit • Installed in BAC valve
• Operates idle-up
Test connector For initial idle speed adjustment • Gerrn, 1-pin
• Idle speed feedback control cancelled when connector grounded
Water thermo sensor Detects coolant temperature; sends
signal to engine control unit
76G04C-078
4C—45

4C
ISC
SYSTEM
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
\Page
Symptom
Air valve P/S pres-sure switch
Solenoid
valve (Idle
speed
control)
Water
thermo
sensor
Engine control unit terminal System
In-
spection
Possible cause
\Page
Symptom
Air valve P/S pres-sure switch
Solenoid
valve (Idle
speed
control)
Water
thermo
sensor
1L 1W 2Q
System
In-
spection
Possible cause
\Page
Symptom 4C—47 4C—97 4C—48 4C—107 4C—98 4C—46
Engine
stalls
During warm up 2 — 3 4 — 5 6 1 Engine
stalls After warm up — 4 2 — 3 5 6 1
Rough
idle
During warm up 2 — 3 — — 4 5 1 Rough
idle After warm up 4 2 — 3 5 6 1
High idle speed after warm up 2 5 3 — 4 6 7 1
Runs rough on deceleration — — 2 — — 3 4 1
Afterburn in exhaust system 2 — 3 — — 4 5 1
Falls emission test 2 3 — — 4 5 1
76g04c-079
System Inspection
(Air valve)
1. Ground the test connector (Green, 1-pin) with a
jumper wire.
2. Disconnect the ISC valve connector (Gray, 2-pin)
at idle while the engine is cold.
3. Note the engine speed and reconnect the con-
nector.
4. Warm up the engine to the normal operating tem-
perature and disconnect the connector again.
5. Check that the engine speed is lower than that
when cold.
4C—46

ISC SYSTEM 4C
76G04C-081
76G04C-082
Cooling fan switch
Rear defroster switch
Head light switch
Blower motor switch
ISC "valve
76G04C-083
(ISC valve)
6. Connect the ISC valve connector.
Note
a) Make sure that the initial idle speed is set
to specification.
b) All accessory must be OFF.
7. Again disconnect the ISC valve connector (engine
at normal operating temperature).
8. Check that the engine speed decreases.
9. Reconnect the ISC valve connector.
10 Remove the jumper wire from the test connector
and make sure that the idle speed is within specifi-
cations.
(Load Test)
11. Apply power steering, electrical, and air conditioner
loads and check that the idle speed is controlled
to within specifications.
Load Idle speed
P/S 750 ± 50
E/L 800 ± 50
A/C 800 ± 50
E/L and A/C 800 ± 50
BAC Valve
Air valve
1. Remove the BAC valve from the throttle body.
2. Blow air through the valve from port A and check
that air comes out of port B when the BAC valve
is cold..
3. If not correct, replace the BAC valve.
Note
Refer to "Installation" on this page for the
BAC valve installation.
86U04A-063
4C—47

FUEL SYSTEM 4C
FUEL SYSTEM
76G04C-087
This system supplies the necessary fuel for combustion at a constant pressure to the injectors. Fuel
is metered and injected into the intake manifold according to the injection control signals from the en-
gine control unit. It consists of the fuel pump, fuel filters, delivery pipe, pulsation damper, pressure
regulator, injectors, fuel pump control unit, and the control relay.
The fuel pump is mounted in the fuel tank to minimize the operating noise of the fuel pump. The injec-
tors directly supplied with battery voltage through the control relay. The connector of the injectors is
white to distinguish the injectors for FE DOHC from those of other engines.
Due to the installation of the steering angle transfer shaft for the 4-wheel steering (4WS) the fuel tank
of 4WS vehicles is designed with separate right and left sections. A transfer pump is used to pump
fuel from the left side to the right side.
4C—49

4C FUEL SYSTEM
COMPONENT DESCRIPTION
Component Function Remark
Air flow sensor Detects amount of intake air;
sends signal to engine control unit
Clutch switch Detects in-gear condition; sends signal to engine control unit Switch ON when clutch pedal released
Engine control unit Detects signals from input sensors and switches; controls injector and fuel pump operations
Fuel filter Filters fuel
Fuel pump Provides fuel to injectors • Operates while engine running
• Installed in fuel tank
Fuel pump control unit (4WS) Monitors fuel level in left section; controls transfer pump operation
G signal pick-up Detects No.1 cylinder TDC; sends signal to engine control unit Installed in distributor
Idle switch Detects when throttle valve fully closed; sends signal to engine control unit Installed on throttle body
Ignition switch (ST position) Sends engine cranking signal to engine control unit
Injector Injects fuel into intake port • Controlled by signals from engine control unit • High-ohmic injector
Intake air thermo sensor Detects intake air temperature; send signal to engine control unit
Control relay Supplies electric current to injectors fuel pump and engine control unit
Ne signal pick-up Detects crank angle at 180° intervals; sends signal to engine control unit Installed in distributor
Neutral switch Detects in-gear condition; sends signal to engine control unit
Switch ON when in gear
Oxygen sensor (Unleaded fuel) Detects oxygen concentration; sends signal to engine control unit
• Zirconia ceramic and platinum coating • Integrated heater coil
Pressure regulator Adjusts fuel pressure supplied to injectors
Pulsation damper Absorbs fuel pulsation
Throttle sensor Detects throttle valve opening angle;
sends signal to engine control unit
Installed on throttle body
Transfer pump (4WS) Pumps fuel from the left to the right side Controlled by fuel pump control unit
Transfer pump switch (4WS) Detects fuel level in left section;
sends signal to control unit
Water thermo sensor Detects coolant temperature; sends signal to engine control unit
Water thermo switch (Unleaded fuel) Detects radiator coolant temperature; sends signal to engine control unit ON: above 17°C (63°F)
76G04C-088
4C-50

FUEL SYSTEM
4C

TROUBLESHOOTING
Checking 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
Troubleshooting
Guide. (Refer
to
page 4C—10,
and 11)

Possible cause 0 CO £ O ** CO £ O "5
Page


o CO c 0> (A
S o c
w O M C
.fc <0 "o
^ o w c 0) <0 c « o>
Im O CO c w w
0>
!
41 10 o E k 0) £ **
d>
5 <0 O E ^ 0) £
w 0

Fuel
pump
Injector Fuel
pressure

Engine control
unit terminal
a. E 3 a
a> » c

Transfer

pump

sv
(4WS)
ha c o o
if Qj
«> S£

< g. X O £ 1-ID a 5
Fuel
pump
Injector Fuel
pressure

1Q 3C,3E 3F,3H 3B ID k_ H
Transfer

pump

sv
(4WS) 3
C
U.
3

Symptom *C—103 4C—110 4C—107 4C—104 4C—107 4C—106 4C-56 4C-57 4C-54 4C-98 40-59
Hard start
or
won't start (Cranks
OK)
— — —-— g — 1 7 — 2 8 6 3 4 5
Engine During warm
up
4 — — — 3 — — 2 1 — 5 — — — —
stalls After warm
up
1 — — — — — — 3 2 — 4 — — — —
Rough During warm
up
5 — — — 3 — — 2 1 — 4 — — — —
a> 3 Idle After warm
up
1 6 — — 4 — — 3 2 — 5 — — — —
•o a> •o (0 a> c -»
Poor acceleration, hesi-tation,
or
lack
of
power 1 — — 3 5 — — 4 2 — 6 — — — — •o a> •o (0 a> c -» Runs
rough on
deceleration 1 — — — — — — 2 — — 3 — — — —
Afterburn on deceleration 1 — — — — — — 2 — — 3 — — — —
Poor fuel consumption 6 — 5 — 4 — — 2 1 — 3 — — — —
Engine stalls
or
runs rough after hot starting 1 5 — — — — — 3 2 — 4 — — — —
Falls emission test — — 1 — — 2 — 3 — — 4 — — — —
Hard start
or
won't
start (Cranks
OK)
— — — — 9 — 1 7 — 2 8 6 3 4 5
Engine During warm
up
4 — — — 3 — — 2 1 — 5 — — — —
stalls After warm
up
1 — — — — — — 3 2 — 4 — — — —
Rough During warm
up
— — — 3 — — 2 1 — 4 — — — —
a> 3 Idle After warm
up
1 6 — — 4 — — 3 2 — 5 — — — —
•o a> •o a
Poor acceleration, hesi-tation,
or
lack
of
power 1 — — — 4 — — 3 2 — 5 — — — —
a> Runs rough on deceleration 1 — — — — — — 2 — — 3 — — — —
Afterburn on deceleration 1 — — — — — — 2 — — 3 — — — —
Poor fuel consumption 5 — — — 4 — — 2 1 — 3 — — — —
Engine stalls
or
runs rough after
hot
staring 1 5 — — — — — 3 2 — 4 — — — —
Falls emission test 1 ?
76G04C-089
4C—51

4C FUEL SYSTEM
FUEL PRESSURE RELEASE AND SERVICING
FUEL SYSTEM
Fuel in the fuel system remains under high pressure
even when the engine is not running.
a) Before disconnecting any fuel line, release the fuel
pressure from the fuel system to reduce the pos-
sibility of injury or fire.
1. Start the engine.
2. Disconnect the 4-pin connector from the con-
trol relay or the fuel pump connector (5-pin or
6-pin).
3. After the engine stalls, turn OFF the ignition
switch.
4. Reconnect the relay or fuel pump connector.
b) Use a rag as protection from fuel spray when dis-
connecting the hoses.
Plug the hoses after removal.
c) When inspecting the fuel system, use the SST.
4C—52

4C FUEL SYSTEM
f-|To pulsation
-'damper
76G04C-092
Pressure regulator
How to Connect Multi-Pressure Tester
Warning
Before connecting the SST, release the fuel
pressure from the fuel system to reduce the
possibility of injury or fire. (Refer to page
4C—52.)
1. Disconnect the negative battery terminal.
2. Disconnect the fuel main hose from the fuel filter.
3. Connect the SST and adapter between the fuel
main hose and the fuel pump.
Caution
Do not reverse the adapter connection.
4. Disconnect the vacuum hose from the pressure
regulator. Connect the SST to the vacuum hose
with a three-way joint.
5. Connect the negative battery terminal.
6. Connect the SST to the battery.
76G04C-093
V „ Test connector (Yellow)
7. Connect the terminals of the test connector (Yel-
low) with a jumper wire. Turn the ignition switch
ON to operate the fuel pump.
8. Check for fuel leaks.
Caution
After checking for fuel leakage, turn the igni-
tion switch OFF and disconnect the jumper
wire from the test connector.
86U04A-072
FUEL PRESSURE
Note
Warm up the engine to normal operating tem-
perature.
Injection Pressure
1. Set the lever on the adapter as shown in the figure.
76G04C-094
4C-54

FUEL SYSTEM 4C
i i 1 1 1 i i
r.:.:::r t t t t t izn —i—i—i—i—i—i—i—i—
2DD 350
86U04A-074
2. Run the engine and measure the injection pres-
sure at various speeds.
Injection pressure: Approx. 235—275 kPa
(2.4—2.8 kg/cm2, 34—40 psi)
3. If not within specification, check the fuel pump pres-
sure and fuel line pressure.
Fuel Pump Pressure
1. Connect the terminals of the test connector (Yel-
low) with a jumper wire.
2. Turn the ignition switch ON to operate the fuel
pump.
3. Set the lever on the adapter as shown in the figure.
4. Check the fuel pump pressure.
Fuel pump pressure: 441—588 kPa
(4.5—6.0 kg/cm2, 64—85 psi)
5. If the fuel pump pressure is not within specifica-
tion, check the following;
No pressure
• Fuel pump operation (Refer to page
4C—56.)
Low pressure
• Fuel pump feeding capacity (Refer to
page 4C—56.)
High pressure
• Replace the fuel pump
6. After checking the fuel pump pressure, disconnect
the jumper wire from the test connector.
Fuel Line Pressure
1. Start the engine and run it idle.
2. Set the lever on the adapter as shown in the figure.
3. Check the fuel line pressure.
Fuel line pressure: Approx. 186—226 kPa
(1.9—2.3 kg/cm2, 27—33 psi)
4. If not within specification, check the pressure regu-
lator vacuum hose.
4C-55