Ignition System - C3I: Description
The Computer Controlled Coil Ignition System (C(3)I) eliminates the need for a mechanical distributor. The C(3)I system works in conjunction with the Computer Command Control System (CCC) to maintain vehicle performance and lower emissions. An Electronic Spark Timing System (EST) is used on C(3)I equipped vehicles.
The C(3)I system consists of an electronic control module (ECM), coil pack, ignition module, and crankshaft and camshaft position sensors. The coil pack contains 3 separate ignition coils. On 3.0L, camshaft and crankshaft sensor is contained in 1 unit, located at the harmonic balancer.
On 3.8L, crankshaft sensor is mounted at the harmonic balancer. Camshaft sensor is located at the camshaft sprocket. The primary function of the ECM is to control spark advance. Timing is controlled by the ECM from the following inputs: crankshaft position, engine speed, engine temperature, and amount of air entering intake manifold.
Input from the sensors is used by the ignition module to determine correct spark plug firing sequence. The ignition module then selects and sequentially triggers each of 3 interconnected coils to fire spark plugs at the proper crankshaft position.
In the C(3)I system, each cylinder is paired with the cylinder that is opposite in the firing order. Cylinders 1-4, 5-2, and 3-6 are paired. The spark occurs simultaneously in the cylinder coming up on compression and in the cylinder coming up on exhaust. The process is repeated when the cylinders reverse roles. Each cylinder pair is fired by its own ignition coil. Ignition coils are mounted on the ignition module.
Ignition timing can also be modified by the Electronic Spark Control System (ESC). This system retards ignition timing to reduce spark knock. The ESC system consists of an ESC module and a knock sensor.