Ford 2003 Mustang Workshop Manual page 929

SECTION 303-00: Engine System — General Information
GENERAL PROCEDURES
Spark Plug —Inspection
1. Inspect the spark plug for a bridged gap.
Check for deposit build-up closing the gap between the electrodes. Deposits are caused
by oil or carbon fouling.
Clean the spark plug.
2. Check for oil fouling.
Check for wet, black deposits on the insulator shell bore electrodes, caused by excessive
oil entering the combustion chamber through worn rings and pistons, excessive valve-to-
guide clearance or worn or loose bearings.
Correct the oil leak concern.
Install a new spark plug.
3. Inspect for carbon fouling. Look for black, dry, fluffy carbon deposits on the insulator tips,
exposed shell surfaces and electrodes, caused by a spark plug with an incorrect heat range,
dirty air cleaner, too rich a fuel mixture or excessive idling.
Clean the spark plug.
2003 Mustang Workshop Manual