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Spark Plug Replacement
How Much Does a Spark Plug Replacement Cost?
The spark plugs are one of the most important components in a petrol internal combustion engine.
Their main job is to ignite the air and fuel mixture inside the cylinders.
The ignition system supplies voltage to the spark plug at specific intervals controlled by the Engine Control Unit or an Ignition module.
They do wear out over time and most manufacturers have specific kilometre and time intervals for replacement.
If they are not replaced, the spark plug will struggle to ignite the air-fuel mixture, causing the engine to misfire and increase fuel consumption.
Most engines will have a spark plug for each cylinder, although some manufacturers will use two spark plugs per cylinder.
On some vehicles, removal of the intake manifold is required to get to the spark plugs.
The average cost to have your spark plugs replaced starts at around $120 up to $400+, depending on the type of spark plugs needed (regular or precious metal) and if other components, such as the inlet manifold, need to be removed to allow access.
What is a Spark Plug?
A spark plug is an electrical conductor, that transfers the electrical current generated by the ignition system into the combustion chamber of the engine.
This current – or ‘spark’ - is what is used to ignite the air/fuel mixture and provide drive from the engine.
If the spark plug is worn excessively or faulty, this mixture will not be combusted efficiently and an engine misfire will result.
This can be felt as a shudder or vibration through the vehicle and the ‘check engine light’ may also illuminate.
Common Signs Your Spark Plugs May Require Replacing
- Check Engine Light is on
- Increased engine vibration or engine misfire
- Decreasing fuel economy
- Poor engine performance
How are the Spark Plugs Replaced?
- The vehicles computer system will be scanned for any Diagnostic Trouble Codes (DTC)
- The bonnet is opened and the surface around the ignition system is cleaned of dirt and debris and inspected for damage
- The inlet manifold is removed (If required)
- The ignition leads or coil packs are disconnected, and the spark plugs removed
- The threads in the cylinder head are inspected for damage
- The old spark plugs are removed and inspected for any signs of damage
- If requested, a compression test may be carried out (at an additional charge)
- The new spark plug gaps are measured and then fitted into the cylinder head
- The ignition leads or coil packs are refitted and the inlet manifold is refitted with new gaskets (If removed)
- The engine is started to ensure correct operation and any DTC’s are cleared from the computer system.
Tips to Remember
- Some manufacturers use spark plugs made of precious metals such as platinum and iridium. These spark plug materials allow for longer intervals between replacement and can often increase the efficiency of the engine. They are more expensive than traditional copper spark plugs.
- Checking of the ignition leads or coil packs is also advised when replacing the spark plugs to ensure all components are in good working condition.
How Important is Replacing Worn Spark Plugs?
Operating a vehicle that has excessively worn spark plugs can cause expensive internal engine damage, and should be inspected and rectified as soon as possible.
If the vehicle is misfiring, it will allow un-burned fuel to enter the exhaust and may cause extensive damage to the catalytic converter and other sensitive engine components.
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