Observation

     The expected responses were:

•        The parts labelled in Fig. 1

                     X  vacuum advance mechanism
Y    ignition coil
Z    ignition control unit / electronic control unit (E.C.U.) / Brain box

•    (i) Function of the plug in operation of the electronic ignition system
• to ignite the air and fuel mixture inside the combustion chamber
• a device for delivering HT electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark

                (ii) Faults on the spark plug that can affect the operation of the electronic ignition  system

• carbon deposits
• ash deposits
• oil deposits
• gap bridging
• too hot condition
• high speed glazing
• detonation
• mechanical damage
• too wide gap
• too small gap
• wet / soaked plug

•       Two component of the distributor
• Contact breaker
• condenser
• rotor
• distributor shaft
• cam lobes
• mechanical advance mechanism segment
• Carbon brush
• Distribution cap
• Segments
• Vacuum advance mechanism

• Description of the operation of the system in the functioning of a motor vehicle

When the ignition switch is put on, current flow from the switch to the coil primary winding which in turn send signal to the ignition module. The ignition module makes and breaks the primary circuit due to the position of the picking coil on the reluctor wheel. The time make and break of the cut induce an emf in the secondary winding which increases the voltage up to 50, 000 V. The high voltage is sent to the distributor which in turn distributes it to the spark plugs according to the firing order.

It was reported that the majority of candidates who attempted this question gave poor responses leading to a below average performance. Although, some candidates were able to properly state the possible faults of a spark plug.