Subaru Legacy 2004 Service Manual page 402

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.
(A)
(B)
(E)
(A) Spark plug gap
(B) Carbon accumulation or wear
(C) Crack
(D) Damage
(E) Damaged gasket
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, dirty air
cleaner, etc.
It is advisable to replace with plugs having hotter
heat range.
Spark Plug
(C)
(D)
IG-00010
IG-00011
IG-00012
IG(H4SO 2.0)-6
3) Oil fouled:
Wet black deposits show excessive oil entrance
into combustion chamber through worn rings and
pistons or excessive clearance between valve
guides and stems. If the same condition remains
after repair, use a hotter plug.
4) Overheating:
White or light gray insulator with black or brown
spots and bluish burnt electrodes indicate engine
overheating. Moreover, the appearance results
from incorrect ignition timing, loose spark plugs,
wrong selection of fuel, hotter range plug, etc. It is
advisable to replace with plugs having colder heat
range.
CAUTION:
Avoid using a plug cleaner because of the
spark plug with a platinum tip. (2.5 L model)
D: ADJUSTMENT
Adjust the spark plug gap, if necessary, by measur-
ing with a gap gauge. (2.0 L model)
Spark plug gap: L
1.0 — 1.1 mm (0.039 — 0.043 in)
L
IG-00013
IG-00014
(A)
IG-00015