1987 MAZDA 626 engine

TROUBLESHOOTING WITH SST 4B
Code No. 28 (Solenoid valve—EGR) PC: Possible Cause
VES

Is there continuity between solenoid valve and engine control unit?
Solenoid valve Control unit
B (WL wire) 2N

NO
PC: Open circuit
in
wiring harness from solenoid
valve
to
engine control unit

YES
PC:
•
Short circuit
in
wiring harness • Engine control unit malfunction

76G04B-019
Code No. 34 (Air bypass solenoid valve—Idle-up C)
YES
PC:
•
Short circuit
in
wiring harness • Engine control unit malfunction

76G04B-020
4B—23

4B TROUBLESHOOTING WITH SST
No. 35 Code (Air bypass solenoid valve—Idle-up B) PC: Possible Cause
YES
PC:
•
Short circuit
in
wiring harness • Engine control unit malfunction

76G04B-021
4B—24

SWITCH MONITOR FUNCTION 4B
SWITCH MONITOR FUNCTION
Individual switches can be monitored by the SST.
Note
The test connector must be grounded and the ignition switch ON (engine stopped).
Control unit
76G04B-022
Switch Self-Diagnosis Checker (Monitor lamp) Remarks Switch Light ON Light OFF Remarks

Clutch switch Pedal released Pedal depressed Gear:
IN

Neutral switch In gear Neutral Clutch pedal released
Idle switch Pedal depressed Pedal released
—

Brake light switch Pedal depressed Pedal released
—

A/C switch ON OFF Blower motor position:
"1"

position
Headlight switch ON OFF
—

Rear defroster switch ON OFF
—

Blower switch ON OFF Blower motor position:
"3"
or
"4"
position
Inhibitor switch D,
1, 2
and
R
range P and
N
range
—

Water thermo switch (Elec-trical fan) Terminal disconnected Terminal connected While fan
not
operating

4B-25

4B SWITCH MONITOR FUNCTION
49 H018 9A1
INSPECTION PROCEDURE
1. Warm up the engine to normal operating temper-
ature and stop it.
2. Connect the SST to the check connector (Green,
6-pin) and the negative battery terminal.
86U04A-034
76G04B-023
3. Connect a jumper wire between the test connec-
tor (Green, 1-pin) and a ground.
4. Turn the ignition switch ON. Check if monitor lamp
illuminates when each switch is made to function
as described below.
Caution
a) If any one of the switches is activated, the
monitor lamp will stay on.
b) Do not start the engine.
Note
The Digital Code Checker (49 G018 9A0) with
the Signal Adapter (49 9200180) may be used
in place of the Self-Diagnosis Checker.
Procedure
76G04B-024
4B—26

IDLE ADJUSTMENT 4B
76G04B-034
76G04B-035
Idle mixture
Automatic
Control
Function
Engine Control Unit

IDLE
ADJUSTMENT
IDLE SPEED
Preparation
1) Check the condition of the engine (plugs, leaks in
hoses, etc.).
2) Make sure all accessories are OFF.
3) Warm up the engine and run it for three minutes
at 2,500—3,000 rpm in neutral.
4) Check the initial ignition timing and adjust if
necessary.
Inspection and Adjustment
Caution
Disconnect the air bypass solenoid connec-
tor when checking and adjusting the idle
speed.
1. Check that the idle speed is within specification.
Specification:
MTX—800 +58 rpm
ATX—900 +58 rpm (P range)
2. If the idle speed is not within specification, remove
the blind cap from the throttle body and adjust it
by turning the air adjust screw.
IDLE MIXTURE
Because an automatic compensation function
for air/fuel mixture is built into the engine con-
trol unit, it is not necessary to check and adjust
the idle mixture.
86U04A-049
4B-29

4B INTAKE AIR SYSTEM
INTAKE AIR SYSTEM
76G04B-036
This system controls the air required by the engine for operation. The system consists of the air duct,
air cleaner, air flow meter, throttle body, dynamic chamber, and intake manifold.
COMPONENT DESCRIPTIONS
Component Function Remarks
Air cleaner
Filters
air
into throttle body

Air flow meter
Detects amount
of
intake air;
sends signal
to
engine control unit Intake
air
thermo sensor and fuel pump
switch are integrated

Throttle body
Controls intake
air
quantity Integrated throttle sensor and idle switch

76G04B-037
4B—30

INTAKE AIR SYSTEM 4B
76G04B-039
D C B E\\ I I A
p 'V > "
F G
76G04B-040
76G04B-041
1. Check that the throttle valve moves smoothly when
the throttle lever is moved from fully closed to fully
open.
2. Warm up the engine and run at idle.
3. Check the vacuum generated at each port as
shown in the following table.

~ —Condition
Port (Connected to) ——____ Idle Other
A (solenoid valve, EGR) No Yes
B (distributor, advance) No Yes
C (EGR modulator valve) No Yes
D (water thermo valve) No Yes
E (vacuum switch valve
&
charcoal canister) Yes
F (distributor, retard
& air
control valve) Yes
G (distributor, advance) Yes

4. If vacuum is not obtained as in the table, clean the
necessary port.
Dynamic Chamber
1. Visually check the dynamic chamber for damage.
2. Replace, if necessary.
Intake Manifold
1. Visually check the intake manifold for damage.
2. Replace, if necessary.
76G04B-042
4B—33

IDLE-UP SYSTEM 4B
IDLE-UP SYSTEM
Dynamic chamber
To engine i
lN
Water thermo |ntake air sensor thermo
sensor
E/L control unit
-D
Solenoid A
From air ^^ flow meter ~
Engine
control
unit
Atmospheric pressure sensor
HI
f
"Solenoid B
UJ m
Solenoid C
u
Adjusting screw
| A/C
H-!
relay
IGN switch
-©n
To engine
control
unit
Magnetic clutch
fftf
tr Main relay
r © ©
P/S pressure switch
76G04B-043
Air Valve
This valve is constructed so that the gate valve is opened and closed by means of a bimetal strip and
heat coil. It acts as a fast idle mechanism by opening the gate valve to increase intake air by bypass-
ing the throttle valve while engine is cold, therefore engine speed is increased to shorten the warm
up period.
Air Bypass Solenoid Valve
This valve incorporates three solenoid valves. They operate according to the signal from the engine
control unit or A/C switch in order to achieve idling stability and the optimum idle speed.
The operating conditions of each solenoid valve are as shown below.
Solenoid valve Operating condition

A A/C operated
B Intake air temp, above 55°C (131 °F)
or
vehicle
at
above 1,000
m
(3,280
ft)

C P/S operated, E/L applied, intake
air
temp, above 55°C (131 °F), pressure regulator solenoid ON
or
vehicle
at
above 1,900
m
(6,232
ft)
4B-35