General System Description

Ignition Control System:

GENERAL DESCRIPTION
The Powertrain Ignition Control System controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture in each cylinder at the correct time. This Ignition Control System has several advantages over a mechanical Distributor Ignition system.
^ No moving parts to wear out.
^ No mechanical load on the engine.
^ Elimination of mechanical timing adjustments.
^ Located for easier service and improved reliability.
^ Improved high engine speed performance.

COMPONENTS
The Ignition Control System consists of the following components:
^ Two crankshaft position sensors ("A" and "B").
^ Crankshaft reluctor ring.
^ Camshaft position sensor.
^ Ignition control module.
^ 4 separate ignition coils.
^ Eight spark plug wires and conduit.
^ Eight spark plugs.
^ Knock sensor.
^ Powertrain Control Module (PCM).

SYSTEM OPERATION
This Ignition Control System does not use a conventional distributor or a single ignition coil. In this ignition system, both ends of each of the four ignition coils are connected to a spark plug. Each coil is connected with spark plugs on "companion" cylinders, i. e., on top dead center at the same time (1 - 4, 2 - 5, 6 - 7, and 3 - 8) . One cylinder is on its compression stroke when the other one is on its exhaust stroke.

Ignition Current Flow:

WASTE SPARK THEORY
When the coil discharges, both plugs fire at the same time by using the engine block to complete the electrical circuit. The cylinder on the compression stroke is called the "event" cylinder and the one on the exhaust stroke is the "waste" cylinder. The two cylinders "share" the energy available from the ignition coil to fire both spark plugs. This method of ignition is called "waste spark" ignition.

Since the polarity of the ignition coil primary and secondary windings does not change, one spark plug always fires with a forward current (center electrode to ground electrode) and its "companion" plug fires with a reverse current (ground electrode to center electrode). This is different from a convention distributor ignition system that fires all the plugs with the same forward current flow.

It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its "companion" spark plug. The disconnected plug wire acts as one plate of a capacitor and the engine block acts as the other plate. These two "capacitor plates" are charged as a spark first jumps across the gap of the connected spark plug. The "plates" are then discharged as the energy is dissipated as the spark continues. Voltage requirements are very high with an "open" spark plug or wire. The ignition coil may have enough reserve energy to fire the connected plug at idle, but possibly not under some engine load conditions. A more noticeable misfire may be evident under load; both spark plugs may then not fire.

Position Sensor Signals:

IGNITION TIMING
^ The Crankshaft Reluctor Ring has 24 evenly spaced notches plus 8 additional notches (shaded) used for synchronization.

^ As the crankshaft rotates, the notches pass the position sensors and create a voltage pulse signal in the sensor that is an input for the Ignition Control (IC) module.

^ Because of the physical location of the two crankshaft position sensors, the signal of "B" lags the signal of "A" by 27 degrees of crankshaft revolution.

^ To synchronize the ignition, the IC module first counts the number of "B" pulses between every 2 "A" pulses. There can be 0, 1 or 2 "B" pulses between "A" pulses.

^ When the IC module sees 0 "B" pulses between "A" pulses, it starts counting "B" pulses between "A" pulses. When the IC module counts exactly 4, it synchronizes the ignition on the very next "A" pulse. If the IC module counts over 4 (jumps from 3 to 5). it waits for another "B" pulse between "A" pulse to start counting again.

^ This process allows the ignition to synchronize and fire the 1st spark plug within 180° (1/2 engine revolution).

^ The camshaft position sensor provides the IC module with cylinder # 1 firing order information, which the PCM uses for sequential fuel injection.

^ Using 3 sensors allows the IC module to maintain ignition synchronization even if one of the 3 sensors fails.