Cherokee, Grand Cherokee, 1999-2005



Battery voltage is supplied to the 6 (8 for the 4.7L) individual ignition coils from the ASD relay. The Power train Control Module (PCM) opens and closes each ignition coil ground circuit at a determined time for ignition coil operation. Base ignition timing is not adjustable. By controlling the coil ground circuit, the PCM is able to set the base timing and adjust the ignition timing advance. This is done to meet changing engine operating conditions.

The ignition coil is not oil filled. The windings are embedded in an epoxy compound. This provides heat and vibration resistance that allows the ignition coil to be mounted on the engine. Because of coil design, spark plug cables (secondary cables) are not used with the 3.7L or the 4.7L engines.