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Spark Plug Replacement

Spark plugs are the reason a petrol powered engine works. They are a part of the all important process known as “fuel, air and spark”. Without one of these components, your car's engine will not be able to work. 

Your spark plugs transmit the voltage sent from the ignition module, creating a spark inside the cylinder and igniting the fuel and air mixture. 

When they start to fail, the engine will run rough as the spark does not provide strong ignition. This can lead to the engine running rich and decreasing your fuel economy. 

What is a spark plug? 

A spark plug is a conductor with a receptor on one end that receives the ignition voltage. This voltage is then transferred to the other end of the spark plug where it flows up a tip and sparks across to a terminal with a gap typically around 1mm. 

When the terminals get worn, the strength of the spark will decrease and this is what leads to misfires and poor running. 

The strength of the spark is determined by the voltage received and the ability to transmit the spark. When one of these factors start to fail, the spark is affected and this affects your engine.

Why do you need new spark plugs?

Old spark plugs won’t transmit the required strength spark. This will reduce your fuel economy as some fuel is left unburnt when it is pumped through the exhaust. This is why you can smell the ‘richness’ when your spark plugs fail. 

Faulty spark plugs can also lead to engine misfires, this causes damage to the engine and can lead to far more serious problems down the road.

What symptoms mean you need new spark plugs

  • Engine is running rough and misfiring
  • Fuel economy is very poor
  • You get an engine warning light
  • There is a clear smell of unburnt fuel
  • The car is down on power

How to change a spark plug

  • The bonnet is lifted and the spark plugs are located
  • Some newer models require the intake manifold to be removed to access the plugs
  • The ignition cable is unplugged
  • The spark plug is unbolted with a spark plug socket and removed
  • The new spark plug is bolted into the socket and the ignition cable is reconnected
  • A diagnostic or road test is performed to ensure everything is in working order

How much does a spark plug replacement cost?

It’s not a terribly hard job and those who are mechanically minded can do it themselves.

The price for new spark plugs starts at around $5 a plug and can go up to $50 for the high performance ones. 

A full replacement from a mechanic can cost in the range of $50 to $350 depending on the level of difficulty of the job.  

How often do I need new spark plugs?

Unless something goes wrong they typically last around 40,000-50,000km

Is a broken spark plug unsafe?

It can be to your wallet. A faulty spark plug can lead to far greater issues with your engine and end up costing you plenty in the long run. 

If there’s something wrong with it then it’s worth sorting out as soon as possible.

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