Subaru Legacy 2005 Service Manual page 1237

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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) Spark plug gap

(B) Carbon accumulation or wear

(E) Damaged gasket

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.

IG(H4DOTC)-5

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.

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)

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