SPARK PLUG TROUBLE TRACER CHART

Fuel Additives Worn-out Spark Plug Ash Deposits

• Appearance: Reddish/brown or purple • Appearance: Centre and/or ground • Appearance: Light brown deposits deposits/coloration on the core nose electrodes are rounded and the gap encrusted on the centre and/or ground insulator is excessive electrode • Cause: Use of fuel additives • Cause: General wear (spark plug has • Cause: Often due to excessive fuel (or • Effect: Misfire. Normally additives are come to the end of its life). However, oil) additives, however, general engine non-conductive; however, some are the greyish tan/white colour indicates wear can have a similar effect and if the deposit build up is excessive that the plug is the correct heat range on the spark plug it can create an earth leakage path for and also that the fuel/ignition systems • Effect: Ash deposits can ‘shield’ the the spark and engine are generally in good spark, leading to misfire problems condition • Remedy: Replace spark plugs and • Remedy: Ensure plug is of the proper ensure that any additives used are • Effect: An increased gap will multiply heat range and check for engine wear compatible the workload on the ignition system and with the engine manufacturer’s ignition may cause misfire, poor fuel economy, and emission systems and added in the and damage to other ignition correct proportion components. • Remedy: Replacement is recommended with new plug of the same heat range

Pre-ignition Corona Discharge Stain Overheating

• Appearance: Melting (or partial melting) • Appearance: Discoloration of the • Appearance: Chalky white insulator of the ground and/or central electrode ceramic insulator, near to the shell (with no tan colouring) pitted or blistered • Cause: Spark plug too hot, air fuel • Cause: Particles of oil/gas (in the spark electrodes. In some cases the insulator mixture excessively lean, incorrect plug well), becoming attracted to the will begin to turn grey or dark blue ignition advance, defective exhaust ceramic by the magnetic field created • Cause: Improper heat range plug, lean re-circulation system, faulty detonation by the high voltage current flowing air fuel mixture, incorrect ignition timing, sensor, cross induction in the spark plug through the spark plug insufficient plug tightening torque and leads or worn engine components • Effect: Not detrimental to spark plug general engine overheating • Effect: In extreme cases engine damage operation • Effect: General poor running conditions will result • Remedy: Ensure that spark plug “well” • Remedy: Identify the cause of • Remedy: Identify the cause and rectify. is clean when installing new spark plugs overheating and rectify. Replace spark Replace spark plugs in line with plugs in line with manufacturer’s manufacturer’s recommendation recommended heat range

Oil Fouling Cold/Carbon Fouling Flash Over

• Appearance: Firing end of spark plug is • Appearance: Soft, black, sooty deposits • Appearance: Black burn marks (carbon ‘wet’ with lubricating oil on the firing end of the plug tracks) running vertically down the • Cause: Usually a sign of advanced • Cause: Rich air-fuel mixture, weak spark plug insulator towards the shell engine wear (excessive volumes of oil ignition, spark plug too cold or repetitive • Cause: Current discharge from the top in the combustion chamber), oil fouling short journeys terminal of the spark plug, down the can also be caused by a fault in the • Effect: Carbon deposits are conductive outside of the insulator to earth; due crankcase breather system and can create earth leakage paths, to poor fitting/worn spark plug boot • Effect: Misfire due to oil deposits often resulting in misfire problems • Effect: Engine misfire covering the firing end of the plug which can lead to catalyst damage • Remedy: Replace the affected plug(s) preventing the spark from ‘jumping • Remedy: Check fuel & ignition systems, and plug lead(s) the gap’ general engine performance and driving • Remedy: Rectify the cause of excessive style before plug replacement. Confirm oil in the combustion chamber and that the spark plug (part number) is replace spark plugs correct for the application

Detonation Spark Plug Tightening Normal Spark Plug Wear/Operation

• Appearance: Light detonation will cause • Appearance: Spark plug gasket has • Appearance: Greyish tan to white colour black/grey spots on the insulator or not been sufficiently crushed (see around the insulator, at the firing end ground electrode. Severe detonation can photographs) • Cause: Confirms that the spark plug is crack or even break the insulator or • Cause: Incorrect tightening of the the appropriate heat range and has been ground electrode spark plug firing correctly. Also indicates that the • Cause: Abnormal combustion, causing • Effect: If the plug is too loose,correct fuel and ignition systems are working pressure spikes/shock waves in the heat dissipation will be prevented, efficiently and the engine is combustion chamber. Can result from: Gasket shape on a mechanically sound correctly tightened plug resulting inoverheating of the plug inoperative exhaust gas re-circulation which can lead to pre-ignition or • Remedy: None required other than to system, defective detonation sensor, detonation problems. Conversely, if the check the spark plug gap and replace lean air fuel mix, incorrect fuel octane plug is too tight, damage may result to in line with manufacturer’s rating or spark advance and loose fitted the insulator and internal components recommendations spark plugs causing operating problems • Effect: Misfire and/or general poor/ • Remedy: Tighten spark plugs to uneven running which may result in the manufacturer’s recommended engine damage torque value • Remedy: Identify the cause and replace the spark plugs