How To Change Spark Plugs

All petrol engines use spark plugs to ignite the fuel-air mixture in the cylinders; these plugs gradually wear out and have to be replaced. How often depends on your manufacturer; see your Haynes Manual for details. Worn spark plugs can cause difficult starting, misfiring, erratic running and poor fuel consumption.

A persistent misfire can also damage the catalytic converter.


You will need the following:


A set of new spark plugs of the correct type, a spark plug socket spanner and a torque wrench, a short length of flexible hose and some copper grease, the Haynes Manual for your car, possibly, a set of feeler blades or a spark plug gap setting tool.



Step 1:

Open the bonnet and remove any obstacles to access the spark plugs - see your Haynes Manual

Step 2:

Brush or blow away any debris from around the spark plugs, then unscrew and remove them.

Step 3:

Use the feeler blades or the gap setting tool to check the electrode gap of the new plugs, if applicable (see your Haynes Manual).

Step 4:

Put a smear of copper grease on the threads of each new plug and screw them into their holes. Use a length of flexible hose to start them off.

Step 5:

Final tightening of the spark plugs should be done using a torque wrench. See your Haynes Manual for the correct torque.

Step 6:

Reconnect the HT leads and refit any other parts that have been removed.