Principles Of Operation

WARNING: This page is about a different car, the 2011 Jaguar XKR, 2011 Jaguar XK, 2010 Jaguar XKR, and 2010 Jaguar XK. However, it is still accessible from the selected car via links, so may be relevant.

The ignition coils are supplied with electrical power from the battery via a 175 A megafuse in the battery junction box (BJB), the central junction box (CJB) and the ignition relay in the power distribution box. The control signal for the ignition relay is supplied by the central junction box (CJB).

The engine control module (ECM) sends a separate signal to each ignition coil to trigger the power stage switching. The engine control module (ECM) calculates the dwell time from the battery voltage and engine speed, to ensure a constant energy level is produced in the secondary coil each time the power stage is switched. This ensures sufficient spark energy is available without excessive primary current flow, which avoids overheating and damage to the ignition coils.

The engine control module (ECM) calculates the ignition timing for individual cylinders from:

Engine speed
Camshaft position
Engine load
Engine temperature
The knock control function
The shift control function
The idle speed control function.