Spark Plugs Diagnostic Chart

DIAGNOSTIC CHART

	Normal		(Life in case of normal use)
			A worn spark plug not only wastes fuel but also
			strains the whole ignition system because the
			expanded gap requires higher voltage.
			It also reduces the engine's efficiency, resulting
			in reduced fuel economy and increased exhaust
			emissions. Moreover, it contributes to pollution
	Using Unleaded Petrol
			generated by exhaust gas.

SYMPTOMS			CAUSES			REMEDY
• Hard starting				• Rich mixture		• Check float level
• Misfiring		CARBON		• Retarded ignition		• Check choke
• Black exhaust smoke				• Low compression		• Check ignition timing
		FOULING		• Too cold a spark plug		• Check air cleaner
						• Check compression
						• Replace spark plug with correct heat range
• Hard starting				• Worn rings		• Replace worn components
• Misfiring				• Worn piston		• Replace spark plug with correct heat range
• Grey / white exhaust smoke		OIL FOULED		• Leaking valve stem seals
• Loss of oil				• Over-filled oil sump
• Misfiring				• Fuel quality		• Replace spark plug
• Hard starting				• Oil leakage		• Change fuel brand
• No starting		DEPOSIT		• Engine operating period		• Repair engine (if need be)

• Misfiring		BREAKAGE
• Engine noise
		OF THE
		INSULATOR

• Sudden change in temperature (Thermal shock)		• Replace spark plug
• Oil leakage		• Check engine condition
• Internal engine stress		• Repair engine (if need be)

• "Pinking" under acceleration or				• Lean mixture		• Check jets are not clogged
climbing hills				• Advanced ignition timing		• Check float level
• Engine run-on after switching off		OVERHEATING		• Too hot a spark plug		• Check ignition timing
						• Replace spark plug with correct heat range
• Misfiring				• Foreign particles inside cylinder		• Replace spark plugs
• Loss of power				• Broken or damaged valve		• Remove foreign or damaged components
• Hard starting		DAMAGED
• Noise in engine
• Hard starting				• Spark plug incorrectly torqued		• Replace spark plugs
• Misfiring		UNDER		• Spark plug only handtightened		• Tighten spark plug to correct torque
• Black exhaust smoke				• Dirt or carbon in threads of cylinder head		• Replace damaged components
		TIGHTENING				• Check compression on all cylinders
• Hard starting				• Normal electrode wear		• Replace spark plug with correct heat range
• Reduced fuel economy				• ± 0.03mm / 1 OOOkm
		WORN		• Fuel deposits (carbon, lead, additives & salts)
• Hard starting				• Lean mixture		• Replace with correct heat range spark plug
• Misfiring				• Advanced ignition timing		• Check air / fuel mixture
		MELTING		• To hot heat range
• Misfiring		BREAKAGE		• Under tightening		• Correct tightening torques
• Loss of power
• Noise in engine		OF THE
		GROUND
		ELECTRODE
• Misfiring		FOULING		• Excess MMT and Ferrocene		• Replace spark plugs with correct heat range
• Hard starting				• Incorrect heat range		• Get to 450°C self cleaning temperature
• Reduced fuel economy		BY FUEL
		ADDITIVE