System Operation: Operation
WARNING: This page is about a different car, the 2017 Jaguar XJ, 2016 Jaguar XJ, 2015 Jaguar XJ, 2014 Jaguar XJ, and 2013 Jaguar XJ. 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 250 A megafuse in the BJB, a 500A megafuse behind the instrument panel and the ignition relay in the EJB. The control signal for the ignition relay is supplied by the ECM.
The ECM sends a separate signal to each ignition coil to trigger the power stage switching. The 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 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.