Ford LSG 875 Service Manual page 75

249
IGNITION SYSTEM
2-19
CLEANING AND INSPECTION (Continued)
GAP BRIDGED
OIL FOULED
IDENTIFIED BY DEPOSIT
BUILDUP CLOSING GAP
BETWEEN ELECTRODES.
CAUSED Bi OIL OR CARBON
FOULING. REPLACE PLUG,
OR, IF DEPOSITS ARE NOT
EXCESSIVE, THE PLUG CAN
BE CLEANED.
IDENTIFIED BY WET BLACK
DEPOSITS ON THE INSULATOR
SHELL BORE ELECTRODES
CAUSED BY EXCESSIVE OIL
ENTERING COMBUSTION
CHAMBER THROUGH WORN
RINGS AND PISTONS,
EXCESSIVE CLEARANCE
BETWEEN VALVE GUIDES AND
STEMS, OR WORN OR LOOSE
BEARINGS. REPLACE THE PLUG.
CARBON FOULED NORMAL
PRE-IGNITION
IDENTIFIED BY BLACK, DRY FLUFFY
CARBON DEPOSITS ON INSULATOR
TIPS, EXPOSED SHELL SURFACES AND
ELECTRODES.
CAUSED BY TOO COLD A PLUG, WEAK
IGNITION, DIRTY AIR CLEANER,
DEFECTIVE FUEL PUMP, TOO RICH A
FUEL MIXTURE, IMPROPERLY OPERAT-
ING HEAT RISER OR EXCESSIVE
IDLING. CAN BE CLEANED.
1DENTlFlED BY LIGHT TAN OR GRAY
DEPOSITS ON THE FIRING TIP.
IDENTIFIED BY MELTED ELECTRODES
AND POSSIBLY BLISTERED INSULATOR.
METALIC DEPOSfTS ON INSULATOR
INDICATE ENGINE DAMAGE.
CAUSED BY WRONG TYPE OF FUEL,
INCORRECT IGNITION TIMING OR
ADVANCE, ~00 HOT A PLUG, BURNT
VALVES OR ENGINE OVERHEATING.
REPLACE THE PLUG.
OVERHEATING
FUSED SPOT DEPOSIT
IDENTIFIED BY A WHITE OR LIGHT
GRAY INSULATOR WITH SMALL
BLACK
OR GRAY BROWN SPOTS
AND WITH BLUISH-BURNT
APPEARANCE OF ELECTRODES.
IDENTIFIED BY MELTED OR
SPOTTY DEPOSITS RESEMBLING
BUBBLES OR BLISTERS.
CAUSED
BY ENGINE OVER-
HEATING,WRONG
TYPE OF
FUEL, LOOSE SPARK
PLUGS, TOO
HOT A PLUG, LOW FUEL PUMP
PRESSURE OR INCORRECT
IGNITION TIMING. REPLACE
THE PLUG.
CAUSED BY SUDDEN
ACCELERATION. CAN BE
CLEANED IF NOT EXCESSIVE,
OTHERWISE REPLACE PLUG.
B4230-2