Ignition Timing (XJS)
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 1990 Jaguar XJ6, 1990 Jaguar XJ-S, 1989 Jaguar XJ6, 1989 Jaguar XJ-S, and 1988 Jaguar XJ6. However, it is still accessible from the selected car via links, so may be relevant.
ECU controls the ignition timing by monitoring intake manifold vacuum, throttle position, engine air, coolant temperature and engine speed. ECU uses information received from crankshaft sensor to monitor engine speed.