Spark Plugs - troubleshooting, carbon deposits, electrodes, etc.

General Automotive Repair

A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed air and fuel by means of an electric spark. Spark plugs have an insulated center electrode which is connected by a heavily insulated wire to an ignition coil or magneto circuit on the outside, forming, with a grounded terminal on the base of the plug, a spark gap inside the cylinder.

As the current of electrons surges across the gap of the spark plug, it raises the temperature of the spark channel to 60,000 K. The intense heat in the spark channel causes the ionized gas mixed with air to expand very quickly, like a small explosion however more known as a combustion. This is the "click" heard when observing a spark, similar to lightning and thunder. A new type of plug called a pulse plug released in 2007 incorporates a peaking capacitor into the plug itself that releases all its contents into the plug gap giving a much more intense spark.

The heat and pressure force the gases to react with each other, and at the end of the spark event there should be a small ball of fire in the spark gap as the gases burn on their own. The size of this fireball or kernel depends on the exact composition of the mixture between the electrodes and the level of combustion chamber turbulence at the time of the spark. A small kernel will make the engine run as though the ignition timing was retarded, and a large one as though the timing was advanced. Wikipedia:Spark Plugs

The general trouble shooting information lists common vehicle symptons with possible solutions and is not for any particular vehicle make and model. For repair info specifically for your make and model please view the main directory.

Normal Spark Plug Condition

• Light Tan or Gray deposits
• Electrode not burned or fouled
• Gap tolerance not changed

Cold Fouling or Carbon Deposits

• Overrich air and fuel mixture: Adjust air and fuel mixture
• Faulty choke: Replace choke assembly
• Clogged air filter: Clean and/or replace air filter
• Incorrect idle speed or dirty carburetor: Reset idle speed and/ or clean carburetor
• Faulty ignition wires: Replace ignition wiring
• Prolonged operation at idle: Shut engine off during long idle
• Sticking valves or worn valve guide seals: Check valve train

Wet Fouling or Oil Deposits

• Worn rings and pistons: Install new rings and pistons
• Excessive cylinder wear: Rebore or replace block
• Excessive valve guide clearance: Worn or loose bearing

Gap Bridged

• Deposits in combustion chamber becoming fused to electrode: Clean combustion chamber of deposits

Blistered Electrode

• Engine overheating: Check cooling system
• Wrong type of fuel: Replace with correct fuel
• Loose spark plugs: Retighten spark plugs
• Over-advanced ignition timing: Reset ignition timing see

Pre-Ignition or Melted Electrodes

• Incorrect type of fuel: Replace with correct fuel
• Incorrect ignition timing: Reset ignition timing
• Burned valves: Replace valves
• Engine Overheating: Check cooling system
• Wrong type of spark plug, too hot: Replace with correct spark plug

Chipped Insulators

• Severe detonation: Check for over-advanced timing or combustion
• Improper gapping procedure: Re-gap spark plugs

Rust Colored Deposits

• Additives in unleaded fuel Try different fuel brand

Water In Combustion Chamber

• Blown head gasket or cracked head Repair or replace Cylinder head or head gasket

General Automotive Repair

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