Ignition System - C3I: Description

Computer controlled coil (C(3)I) ignition system eliminates the need for a mechanical distributor. The C(3)I ignition system consists of a coil pack, an ignition module, camshaft and crankshaft position sensors or a combination sensor, the necessary wiring, as well as the Electronic Spark Timing (EST) portion of the Electronic Control Module (ECM).

This system utilizes the EST signal from the ECM to control spark timing. Ignition timing is controlled by the ECM by using information from the following inputs: crankshaft position, camshaft position, engine RPM, engine temperature, induction air temperature, throttle position, knock retard (ESC), vehicle speed, gear position, and the amount of air entering the 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 ignition system, each cylinder is paired with the cylinder that is opposite in the firing order. Cylinders No. 1-4, 5-2, and 3-6 are paired. The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke. The process is repeated when the cylinders reverse roles. Each cylinder pair is fired by its own ignition coil.