Subaru IMPREZA 2004 Service Manual page 9

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 gray
brown spots and bluish burnt electrodes indicates
engine overheating. Moreover, the appearance re-
sults 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.
D: CLEANING
Clean the spark plugs in a sand blast type cleaner.
Avoid excessive blasting. Clean and remove the
carbon or oxide deposits, but do not wear away ce-
ramic insulator.
If deposits are too stubborn, replace the plugs.
E: ADJUSTMENT
Correct it if the spark plug gap is measured with a
gap gauge, and it is necessary.
Spark Plug
Spark plug gap: L
With catalyst:
1.0 — 1.1 mm (0.039 — 0.043 in)
Without catalyst:
0.7 — 0.8 mm (0.028 — 0.031 in)
IG-00026
NOTE:
Replace with a new spark plug if this area (A) is
worn to "ball" shape.
IG-00027
IG(H4SO)-7
IGNITION
L
(A)
IG-00028