DISTRIBUTOR CAP
Sits on top of distributor to protect its parts.

FOULING (CARBON/FUEL)
Occurs when the Heat Range of plug is not suitable for the conditions. The temperature at the plug tip is not hot enough to burn off the carbon or fuel.

GAPPING
The distance between the centre and ground electrodes is called the gap. This gap must be a particular distance for the engine to run efficiently. DENSO Spark Plugs are sold pre-gapped and so do not need to be changed. Do not alter the gap of Iridium plugs as the small centre electrode is fragile and could be damaged.

IGNITION COIL
Transforms the relatively small amount of electrical voltage (12-14V) from the battery to a big enough voltage (15,000V to 60,000V) to jump the spark plug gap. Distributorless systems have an electronic coil module.

MISFIRES
Occurs when not enough voltage has been applied to the combustion chamber at the correct time to burn all of the fuel/air mix. Can lead to reduced performance and is detrimental to fuel economy.

PRE-IGNITION
Situations where Ignition of the fuel/air mixture occurs before it is supposed to. Indicates the combustion chamber is too hot. The heat range of the plug may be too hot for the application.

PROJECTED INSULATOR NOSE SPARK PLUGS
In these plugs, the insulator nose projects past the housing end. The insulator nose is around the centre electrode. Because the spark is projected deep into the combustion chamber, faster and more complete combustion is possible. This means improved ignitability. The projected insulator also keeps the heat at idling, providing good anti-fouling properties.