Subaru 2009 IMPREZA, Service Manual

Page: 392 / 3619

IG(H4SO)-5
Spark Plug
IGNITION
C: INSPECTION
Check the electrodes and inner and outer ceramic
insulator of plugs, noting the type of deposits and
the degree of electrode erosion.
1) Normal:
Brown to grayish-tan deposits and slight electrode
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 and dirty
air cleaner.
3) Oil fouled:
Wet black deposits show oil entrance into the com-
bustion chamber through worn rings or pistons, or
excessive clearance between valve guides and
stems.
4) Overheating:
White or light gray insulator with black or brown
spots and bluish burnt electrodes indicate engine
overheating, incorrect ignition timing, wrong selec-
tion of fuel, and loose spark plugs.
D: ADJUSTMENT
Clean spark plugs with a nylon brush, etc. Clean
and remove the carbon or oxide deposits. If depos-
its are too stubborn, replace the spark plugs. After
cleaning the spark plugs, measure the spark plug
gap using a gap gauge.
NOTE:
• Never use plug cleaner.
• Do not use metal brush or it will wear insulator.
Spark plug gap L:
1.0 — 1.1 mm (0.039 — 0.043 in)
(A) Spark plug gap
(B) Carbon accumulation or wear
(C) Cracks
(D) Damage
(E) Damaged gasket
IG-00010
(A)
(B)
(C)
(D)
(E)
IG-00011
IG-00012
IG-00013
IG-00014
IG-02035
L