General System Description

PFI Distributor Ignition Circuit:

DISTRIBUTOR IGNITION COMPONENTS
The Ignition Control System controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture in each cylinder at the correct time. To provide improved engine performance, fuel economy, and control of exhaust emissions, the Powertrain Control Module (PCM) controls distributor timing (spark advance or retard) with the Ignition Control System.

^ Distributor housing
^ Timer Core
^ Camshaft Position sensor, mounted in the distributor, for use by the PCM for control of Sequential Multi-Port Fuel Injection
^ Ignition Control Module (ICM)
^ Eight spark plug wires and conduit
^ Eight spark plugs
^ Pole piece
^ Powertrain Control Module (PCM)
^ Pickup coil
^ Distributor cap and rotor
^ Ignition coil

This system controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture at the correct time. To provide improved engine performance, fuel economy, and control of exhaust emissions, the PCM controls distributor spark advance (timing) with the Ignition Control System.

NOTE: The Distributor Ignition (DI) system was previously known as High Energy Ignition (HEI) system. The two systems are identical.


COMPONENT DESCRIPTION
The magnetic pick-up coil assembly contains a permanent magnet, a pole piece with internal teeth, and a pick-up coil. A toothed timer core, attached to the distributor main shaft, rotates inside the pole piece. As the teeth of the timer core line up with the teeth of the pole piece, a varying current is induced in the pick-up coil. The induced current flow is converted by the IC module into a distributor reference pulse. The IC module, acting as the electronic ON/OFF switch, controls the current flow in the primary winding of the ignition coil. This switching action induces a high voltage in the ignition coil secondary winding which is directed through the rotor and secondary leads to fire the spark plugs.

A hall effect switch, positioned inside the distributor, serves as a cam position sensor for the sequential port fuel injection. The hall switch senses the opening point of the intake valve on the number one cylinder and provides that information to the PCM.

SPARK TIMING CONTROL
All spark timing changes in the Distributor Ignition System are performed electronically by the PCM. The PCM monitors information from various engine sensors and uses this information to compute the desired spark timing and signals the distributor accordingly. A backup spark advance system is programmed in the the ignition module in case of PCM failure.

PURPOSE
Ignition Control (IC) is PCM or Computer Controlled Ignition. Its purpose is for the PCM to control the spark which ignites the air/fuel mixture at a calculated crankshaft position for each cylinder of the engine.

OPERATION
The PCM receives engine speed (RPM) from the IC module, coolant temperature from the ECT, and Manifold Absolute Pressure from the MAP sensor. From this information the advance or retard of the spark is calculated. The ignition control line of the IC module (CKT 423) is used by the PCM to trigger the IC module when the PCM is controlling spark timing.


LOCATION
The IC module is located inside the Distributor and is serviced separately.