Exhaust MAZDA 626 1987 Repair Manual

4A TROUBLESHOOTING GUIDE
FE 8VALVE—UNLEADED FUEL
The Troubleshooting Guide lists the systems most likely to cause a given symptom. After finding the
system(s) to check, refer to the pages shown for detailed guides for each system.
V POSSIBLE CAUSE
\ PAGE
SYMPTOM
Air

cleaner

(Air

cleaner

element)

Idle

adjustment

Fuel

system
(Carburetor,

Fuel

pump)
PTC

heater

system

Air

injection
system

Positive

crankcase

ventilation

system

Deceleration

control
system
Exhaust
gas

recirculation

(EGR)
system

Exhaust

system
Intake
air

temperature

control
system

Idle-up

control

system
Purge

control

system
Auto-return
choke
system
V POSSIBLE CAUSE
\ PAGE
SYMPTOM 4A-23 4A-38 4A-24 4A—42 4A-58 4A—67 4A—45 4A-96 4A-97 4A—60 4A—68 4A--63 4A—40
1 Hard start or won't start
(Cranks OK) 1 2
2 Engine stalls During warm up 6 1 2 5 3 4 2 Engine stalls After warm up 4 2 3 1
3 Rough Idle During warm up 5 1 2 4 3 6 3 Rough Idle After warm up 4 2 3 1
4 High idle speed after warm up 1 5 4 3 2
5 Poor acceleration, hesitation, or lack of power 1 2 5 3 4
6 Runs rough on deceleratio 2 1
7 Afterburn in exhaust system 2 1
8 Poor fuel consumption 4 1 2 3 5
9 Fails emission test 5 1 6 4 3 2
76G04A-020
The numbers of the list show the priorities of inspections from the most possible to that with the lowest
possibility.
These were determined on the following basis:
• Ease of inspection • Most possible system • Most possible point in system
TROUBLESHOOTING PROCEDURE:
1st Check the following items:
Electrical system
1) Battery condition
2) Fuses
Intake air system
1) Vacuum or air leakage
2) Vacuum hose routing
3) Accelerator cable
4) Choke cable
2nd Check the Fuel and Emission Control Systems
Ignition system
1) Spark plugs
2) Ignition timing
Engine
1) Compression
2) Overheating
Fuel system
1) Fuel level
2) Fuel leakage
3) Fuel filter
4) Idle speed
Others
1) Clutch slippage
2) Brake dragging
4A-22

FUEL SYSTEM 4A
TROUBLESHOOTING
POSSIBLE CAUSE
\ PAGE Carburetor Fuel pump Separator
Two-way check valve (Except Middle East) Three-way check valve (Middle East)
SYMPTOM 4A—26 4A—35 4A—37 4A—37
1 Hard start or won't start (Cranks OK) 2 1
2 Engine stalls During warm up 2 1 2 Engine stalls After warm up 2 1
3 Rough idle During warm up 2 1 3 Rough idle After warm up 2 1
4 High idle speed after warm up 1
5 Poor acceleration, hesitation, or lack of power 2 1
6 Runs rough on deceleration 1
7 Afterburn in exhaust system 1
8 Poor fuel consumption 1 2 3
9 Fails emission test 1
76G04A-026
4A-25

4A
IDLE
SPEED AND
IDLE
MIXTURE
76G04A-059
76G04A-060
76G04A-061

IDLE
SPEED AND IDLE MIXTURE
ADJUSTMENT
Note
a) Before adjusting the idle speed and idle
mixture, be sure the ignition timing, spark
plugs, carburetor float level, etc., are all in
normal operation condition.
b)Turn off all electrical loads.
c) This adjustment must be done while the fan
motor is not operating.
Idle Speed
1. Connect a tachometer to the engine.
2. Warm up the engine, and check that the choke
valve has fully opened.
3. Check the idle speed.
Specification
MTX ATX (in N range)
Specification Others
FE 8Valve Unleaded fuel F6 F8 & FE
Idle speed rpm 800 +6S 850 +5S 950 +5o° 900 +5§
4. If not within specification, adjust the idle speed by
turning the throttle adjust screw.
Caution
After adjusting the idle speed, the dashpot ad-
justment should be checked and adjusted if
necessary.
Idle Mixture
[Except FE 8Valve—Unleaded Fuel]
Adjust the idle mixture as follows, after adjusting the
idle speed.
1. Disconnect the secondary air hoses from the reed
valves and plug them. (If equipped.)
2. Insert an exhaust gas analyzer into the tail pipe and
measure the CO concentration.
CO concentration: 2.0 ± 0.5%
3. If not within the specification, remove the blind cap
from the mixture adjust screw.
76G04A-062
4A—38

IDLE SPEED AND IDLE MIXTURE 4A
76G04A-063
76G04A-064
4. Turn the mixture adjust screw to adjust the CO con-
centration.
5. Recheck the idle speed.
6. Fit a new blind cap onto the mixture adjust screw.
Idle Mixture [FE 8Valve—Unleaded Fuel]
Adjustment of the idle mixture is normally un-
necessary.
But if it is necessary, adjust it as follows.
Note
Do not insert the exhaust gas analyzer into the
tail pipe.
Before adjust the idle mixture, check and set
the idle speed.
1. Disconnect the secondary air hoses.
2. Insert an exhaust gas analyzer into the hose and
plug it to prevent leakage.
3. Start the engine and run it at idle.
4. Measure the CO concentration.
5. Remove the blink cap from the mixture adjust
screw.
6. Turn the mixture adjust screw and adjust the CO
level.
CO concentration: 2.0 ± 0.5%
7. If the idle speed fails to meet specification as the
result of the above steps, adjust the idle.
8. Reconnect the secondary air hoses.
9. Fit a new blind cap onto the mixture adjust screw.
76G04A-065
4A-39

4 A DECELERATION CONTROL SYSTEM
TROUBLESHOOTING
Check the condition of the wiring harness and connectors before checking the engine control unit
or switches.
FE 12Valve and F8 (ECE, Hong Kong and Singapore)—MTX
Possible cause
Page
Symptom

Anti-afterburn

valve
Dashpot Bypass
air
control
system
Idle

switch
main
air

bleed

control
system

Engine

control

unit

terminal
Possible cause
Page
Symptom

Anti-afterburn

valve
Dashpot Bypass
air
control
system
Idle

switch
main
air

bleed

control
system
E L M
Possible cause
Page
Symptom 4A—50 4A—50 4A—48 4A—93 4A—51 4A—88
Runs rough on deceleration 2 1 3 5 4
Afterburn in exhaust system 1 2 4 3 5 6
Poor fuel consumption 1 2 3
Fails emission test 7 6 1 2 3 4 5
High idle speed after warm up 1 2 3
Engine stalls during warm up 1
Rough idle during warm up 1
Poor acceleration, hesitation, or lack of power 1
76G04A-079
FE 12Valve and F8 (ECE, Hong Kong and Singapore)—ATX
Possible cause o> o 4-* uT u. E 3
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Symptom 4A—50 4A—48 4A—51 4A—93 4A—86
Runs rough on deceleration 2 3 1 5 4
Afterburn in exhaust system 1 2 3 4 5
Poor fuel consumption 1 2
Fails emission test 7 6 2 1 3 4 5
High idle speed after warm up 1 2
Engine stall during warm up 1
Rough idle during warm up 1
Poor acceleration, hesitation, or lack of power 1
76G04A-080
4A—46

DECELERATION CONTROL SYSTEM 4 A
FE 8Valve—Unleaded Fuel
Possible cause
\Page ^s^
Symptom

Slow

fuel
cut
system
Coast
enrichment
system
Idle

switch
Anti-afterburn
valve

Bypass

air
control

system
Dashpot
(only
MTX)
Engine
control
unit

terminal

Possible cause
\Page ^s^
Symptom

Slow

fuel
cut
system
Coast
enrichment
system
Idle

switch
Anti-afterburn
valve

Bypass

air
control

system
Dashpot
(only
MTX)
A C G I
Possible cause
\Page ^s^
Symptom 4A-53 4A-54 4A-93 4A-50 4A-48 4A-50 4A—91
Runs rough on deceleration 8 6 1 7 3 4 5 2
Afterburn in exhaust system 7 3 1 4 2 5 8 6
Poor fuel consumption 2 1 6 5 4 3
High idle speed after warm up 2 1 3
Fails emission test 4 2 1 5 3 6 7 8 9
76G04A-081
FE 8Valve (General)
Possible cause main air bleed control
solenoid valve
Engine control unit terminal
Possible cause main air bleed control
solenoid valve
MTX ATX
Possible cause main air bleed control
solenoid valve
E F B 2F j 21
Page 4A—51 4A—90 4A—89
Checking order 1 2
76G04A-082
F6 (Singapore)
Possible cause
X^Page
Symptom

Dashpot

(Only

MTX)
Anti-afterburn
valve

idle

switch
L
Coasting

leaner

solenoid

valve
Engine

control

unit

terminal

Possible cause
X^Page
Symptom

Dashpot

(Only

MTX)
Anti-afterburn
valve

idle

switch
L
Coasting

leaner

solenoid

valve
B D
Possible cause
X^Page
Symptom 4A—50 4A—50 4A—93 4A—56 4A—92
High idle speed after warm up 1
Runs rough on deceleration 1 2 3
Afterburn In exhaust system 5 4 1 2 3
Fails emission test 4 1 2 3
76G04A-083
4A—47

DECELERATION CONTROL SYSTEM 4 A
SLOW FUEL CUT SYSTEM [FE 8VALVE—UNLEADED FUEL]
76G04A-096
This system shuts the primary slow fuel passage to prevent run-on and overheating of the exhaust
system when the ignition switch is turned OFF or during deceleration (engine speed above 2,300
rpm and idle switch ON). The slow fuel cut solenoid is actuated by the engine control unit and ignition
switch.
Troubleshooting
Note
Make the system inspection first. If no problem is found, continue with the next inspec-
tion of the Troubleshooting Guide. (Refer to page 4A—47.)
Possible cause System inspection Slow fuel cut solenoid valve
Page 4A—53 4A—34
Check order 1 2
System Inspection
1. Warm up the engine and run it at idle.
2. Connect a tachometer to the engine.
3. Connect a voltmeter to the carburetor connector
terminal (BW wire).
4. Increase the engine speed to 4,000 rpm; then re-
lease the throttle lever.
5. Measure the terminal voltage.
Engine speed Voltage
Above approx. 2,300 rpm Approx. 12V
Below approx. 2,300 rpm Below 1.5V
76G04A-097
4A-53

4A DECELERATION CONTROL SYSTEM
COASTING LEANER SYSTEM (F6 SINGAPORE MTX)
Coasting leaner
0 oAir
a n, © © Battery Ignition
switch Secondary
throttle valve
| / Relay
Engine control unit
Ignition coil
76G04A-102
This system consists of the coasting leaner solenoid valve, engine control unit, ignition coil, and idle switch.
When the idle switch is ON and the engine speed is more than approx. 2,100 rpm (deceleration),
the coasting leaner solenoid valve opens the air passage port to prevent afterburn in the exhaust system.
Troubleshooting
Note
Make the system inspection first. If no problem is found, continue with the next inspec-
tion of the Troubleshooting. (Refer to page 4A—47)
Possible cause System inspection Coasting leaner solenoid valve Relay
Page 4A—56 4A—57 4A—57
Checking order 1 2 3
Coasting leaner System Inspection
1. Warm up the engine and run it at idle.
2. Connect a tachometer to the engine.
3. Connect a voltmeter to the coasting leaner sole-
noid valve connector (LgB wire).
76G04A-103
4A—56

4A
AIR
INJECTION SYSTEM
AIR INJECTION SYSTEM (EXCEPT GENERAL AND MIDDLE EAST)
Reed valve
76G04A-107
To achieve oxidization of CO and HC, the reed valve injects secondary air into the exhaust manifold.
TROUBLESHOOTING
Possible cause
Reed valve Air injection
\ Page pipe
Symptom 4A—59 4A—59
Fails emission test 1 2
76G04A-108
4A-58

AIR
INJECTION SYSTEM 4A
76G04A-109
Reed Valve
1. Warm up the engine to the normal operating tem-
perature, and then stop the engine.
2. Remove the air cleaner cover and element.
3. Start the engine and run it at idle.
4. Place a thin paper over the reed valve inlet port
and check that air is pulled in.
5. Increase the engine speed to 1,500 rpm and
check that there is no exhaust gas leakage at the
inlet by placing a thin paper over the port.
6. Replace the reed valve, if necessary.
76G04A-110
Air Injection Nozzle and Pipe
1. Disconnect the hoses from the air cleaner.
2. Loosen the nuts and remove the air injection noz-
zle and air pipe.
3. Visually check the air injection nozzle and pipe.
4. Replace if necessary.
76G04A-111
4A-59