Electronic Ignition (EI) System

ELECTRONIC IGNITION (EI) SYSTEM
The Electronic Ignition (El) system, commonly referred to as Distributorless Ignition System (DIS), does not use the conventional distributor and coil. This ignition system consists of two separate ignition coils, electronic Ignition Control Module (1CM), and Crankshaft Position (CKP) sensor as well as the related connecting wires and the Ignition Control (IC) portion of the PCM.
A distributorless ignition system such as this one uses a "waste spark" method of spark distribution. Each cylinder is paired with the opposite cylinder in the firing order (1 and 4 or 2 and 3). Spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke.
The cylinder on the exhaust stroke requires very little of the available energy to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverse roles.
It is possible in a no-load condition for one plug to fire, even though the spark plug lead from the same coil is disconnected from the other spark plug. The disconnected spark plug lead acts as one plate of a capacitor, with the engine being the other plate. These two "capacitor plates" are charged as a current surge (spark) jumps across the gap of the connected spark plug. The "plates" are then discharged as the secondary energy is dissipated in an oscillating current across the gap of the spark plug still connected. Because of the direction of current flow in the primary winding and thus in the secondary winding, one plug will fire from the center electrode to the side electrode while the other will fire from the side electrode to the center electrode.
These systems use the same Ignition Control (IC) signal from the PCM as distributor-type ignition systems to control spark timing.
Under 400 RPM, the Ignition Control Module (ICM) controls spark timing (module timing mode). Over 400 RPM, the PCM controls spark timing (IC mode).

To properly control ignition timing, the PCM relies on the following information:
- Engine load (manifold pressure or vacuum)
- Atmospheric (barometric) pressure
- Engine temperature
- Manifold air temperature
- Crankshaft position
- Engine speed (RPM)