Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 110
IG(STI)-4
Spark Plug
IGNITION
2. Spark Plug
A: REMOVAL
Spark plug:
Refer to “SPECIFICATION” for the spark
plug. <Ref. to IG(STI)-2, SPECIFICATION,
1. RH SIDE
1) Disconnect the ground cable from battery.
2) Remove the air cleaner case. <Ref. to IN(STI)-8,
3) Disconnect the connector from ignition coil.
4) Remove the ignition coil.
NOTE:
Turn #3 ignition coil by 180 degrees to remove it.
5) Remove the spark plug with a spark plug socket.
2. LH SIDE
1) Remove the battery. <Ref. to SC(STI)-27, RE-
2) Remove the secondary air pump. <Ref. to
EC(STI)-27, REMOVAL, Secondary Air Pump.>
3) Remove the bolts that secure the air duct to the
rocker cover LH, and lift the air duct.
4) Disconnect the connector from ignition coil.
5) Remove the ignition coil.
NOTE:
Turn #4 ignition coil by 180° to remove it.
6) Remove the spark plug with a spark plug socket.
IN-00203
IG-02127
IG-02072
IG-02149
IG(STI)-5
Spark Plug
IGNITION
B: INSTALLATION
1. RH SIDE
Install in the reverse order of removal.
Tightening torque (Spark plug):
21 N·m (2.1 kgf-m, 15.5 ft-lb)
Tightening torque (Ignition coil):
16 N·m (1.6 kgf-m, 11.8 ft-lb)
2. LH SIDE
Install in the reverse order of removal.
Tightening torque (Spark plug):
21 N·m (2.1 kgf-m, 15.5 ft-lb)
Tightening torque (Ignition coil):
16 N·m (1.6 kgf-m, 11.8 ft-lb)
Tightening torque (Air duct):
6.4 N·m (0.7 kgf-m, 4.7 ft-lb)
C: INSPECTION
1) Check the spark plug for abnormalities. If defec-
tive, replace the spark plug.
2) Check the spark plug electrode and condition of
the insulator. If abnormal, check and repair the
cause and replace the spark plug.
(1) Normal:
Brown to grayish-tan deposits and slight elec-
trode wear indicate correct spark plug heat
range.
(2) Carbon fouled:
Dry fluffy carbon deposits on insulator and elec-
trode are mostly caused by slow speed driving
in the city, weak ignition, too rich fuel mixture,
etc.
(3) Oil fouled:
Wet black deposits show oil entrance into com-
bustion chamber through worn piston rings or
increased clearance between valve guides and
valve stems.
(4) Overheating:
A white or light gray insulator with black or
brown spots and bluish burnt electrodes indi-
cate engine overheating, wrong selection of fu-
el, or loose spark plugs.
(A) Terminal damage
(B) Crack or damage in insulator
(C) Damaged gasket
IG-02094
(C)
(A)
(B)
IG-00011
IG-00012
IG-00013
IG-00014
IG(STI)-6
Spark Plug
IGNITION
3) Using a nylon brush, etc., clean and remove the
carbon or oxide deposits from the spark plug. If de-
posits are too stubborn, replace the spark plugs.
After cleaning the spark plugs, check the spark
plug gap “L” using a gap gauge. If it is not within the
standard, replace the spark plug.
NOTE:
• Never use a plug cleaner.
• Do not use a metal brush as it may damage the
electrode area.
Spark plug gap L:
Standard
0.7 — 0.8 mm (0.028 — 0.031 in)
IG-02095
L
IG(STI)-7
Ignition Coil
IGNITION
3. Ignition Coil
A: REMOVAL
Direct ignition type is adopted. Refer to “Spark
Plug” for removal procedure. <Ref. to IG(STI)-4,
B: INSTALLATION
Install in the reverse order of removal.
Tightening torque:
16 N·m (1.6 kgf-m, 11.8 ft-lb)
C: INSPECTION
For inspection procedure, refer to “Diagnostics for
Engine Starting Failure”. <Ref. to EN(H4DOTC)(di-
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