Spark Plug / Spark Function The spark plug works to burn fuel and air mixture into the combustion chamber (ignition) and then send heat energy out of the combustion chamber (transfer). The spark plug also serves as an indicator for the combustion engine. Spark Plug Maintenance Conduct routine surveys every 4,000 km and replace your spark plugs every 8,000 km (with regular care and normal use). Measure the gap between the ground and the center of the electrode is greater than 1 mm, then replace the spark plug.