Subaru Legacy (2005 year). Manual - part 307
IG(H4DOTC)-5
IGNITION
Spark Plug
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, dirty air
cleaner, etc.
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.
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 or
wrong selection of fuel.
D: ADJUSTMENT
Clean the spark plugs using a wire brush.
Clean and remove the carbon or oxide deposits.
But do not wear away ceramic insulator.
If deposits are too stubborn, replace the plugs.
NOTE:
Do not use a plug cleaner because the spark plugs
are applied with iridium tip.
Spark plug gap L:
0.7 — 0.8 mm (0.028 — 0.031 in)
(A) Spark plug gap
(B) Carbon accumulation or wear
(C) Crack
(D) Damage
(E) Damaged gasket
IG-02010
(A)
(B)
(E)
(C)
(D)
IG-00011
IG-00012
IG-00013
IG-00014
IG-02035
L