Ignition Coil On-Plug And Spark Plug

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

The ignition coil on-plugs are installed in the cylinder head covers, under the Noise, Vibration and Harshness (NVH) covers. Each ignition coil on-plug locates on a spark plug and is secured to the related cylinder head cover with a single bolt. Each ignition coil on-plug incorporates a 3 pin electrical connector for connection to the engine harness.

Each ignition coil on-plug contains a primary and a secondary winding. The primary winding receives electrical power from the ignition relay in the Engine Junction Box (EJB). A power stage in the primary winding allows the PCM  to interrupt the power supply, to induce a voltage in the secondary winding and thus the spark plug. A diode in the ground side of the secondary winding reduces any undesirable switch-on voltage, to prevent misfiring into the intake manifold. The power stage limits the maximum voltage and current in the primary winding, to protect the power stage and limit the voltage in the secondary winding.

The spark plugs are installed one per cylinder, between the inlet and exhaust valves. The spark plugs feature an iridium-tripped center electrode, and a platinum-tripped ground electrode. The energy stored in the ignition coil on-plug, manifests itself on the spark plug in terms of a voltage differential between the electrodes. When the voltage differential equals the required voltage, then the spark plugs and the stored energy is dissipated.