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Replacing spark plugs and spark plug wires

September 27, 2010

Spark plugs are a very important component on any petrol engine. Bad spark plugs can result to poor performance, lack of power, misfiring, excessive fuel consumption or failure to start the engine. A well tuned engine will rarely need spark plug replacements and will only need regular check up every three months. Improperly tuned cars can cause spark plugs to foul up or deteriorate prematurely.

Spark plug wires on the other hand need not be changed as often as spark plugs. They only need to be changed when they have physical defects as they can cause problems such as engine misfire. The wires carry the high-voltage electricity produced by the ignition coil to the terminal of the spark plug. Once at the plug, the electricity travels to the other end of the plug, and jumps a gap between electrodes to produce the “spark” that ignites the fuel mixture.


  • Spanking new spark plug wires (bought mine from Quest Car Parts Ltd, Baricho road, Nairobi. They stock after market wires manufactured by Topran Germany. The OEM wires (original wires) are double the price!!!)
  • Spark plugs (bought Bosch WR7CC, gap pre-adjusted to vehicle’s specifications)
  • Spark plug wrench
  • Good pair of hands

Replacing the spark plugs

  • Locate a spark plug and remove the spark plug wire from that plug
  • Use the spark plug wrench to loosen the plug and proceed to remove it completely by hand
  • Get new spark plug (do not remove washer) and screw it back in by hand before torquing it to specification (still not sure what it is, just made sure it was tight enough)
  • Repeat procedure for all other plugs

Replacing the spark plug wires

  • IMPORTANT: Replace the wires one by one by removing an old one, identifying a new one of similar length and plugging it back in
  • Repeat for all other four wires on distributor
  • Failure to replace wires correctly (where they belong) will cause engine to stutter and misfire

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