Ignition System: Description and Operation

DESCRIPTION

Powertrain Control Module:

This system does not use a stand-alone Ignition Control Module (ICM). The ICM has been integrated into the Powertrain Control Module (PCM). The Profile Ignition Pickup (PIP), Spark Output (SPOUT), Ignition Ground (IGN GND), and Ignition Diagnostic Monitor (IDM) circuits have also been enclosed in the PCM. The functionality of the Ignition System remains the same.

CONSTRUCTION
The Integrated Electronic Ignition (EI) system consists of a Crankshaft Position Sensor (CKP), a PCM, and connecting wiring harnesses. Six cylinder applications use a six tower coil pack. Eight cylinder and dual plug applications use two four tower coil packs.

OPERATION
The EI High Data Rate system eliminates the need for a distributor by using multiple coil packs. Each coil within the pack fires two spark plugs at the same time. The plugs are paired so that as one fires during the compression stroke, the other fires during the exhaust stroke. The next time the coil is fired, the plug that was on exhaust will be on compression and the plug that was on compression will be on exhaust.

The CKP is used to indicate crankshaft position and speed information to the PCM. By sensing a missing tooth on a trigger wheel mounted on the crankshaft damper, the CKP is also able to identify a specific point in the travel of piston 1. The PCM uses the information from the CKP to generate an internal PIP signal.

Once the PIP signal is generated, fuel and spark functions are enabled. The calculated spark target is used internally by the PCM as a pulse width modulated digital signal called the SPOUT. The PCM decodes the SPOUT signal and fires the next spark at the commanded spark target. The PIP signal is also used to supply a clean, inverted signal PIP for tachometer operation.

The PCM also serves as an electric switch for a coil primary circuit. When the switch closes, current flows and a magnetic field expands around the primary coil. When the switch opens, the field collapses and causes the secondary coil to fire the spark plugs at high voltage. In addition, an IDM signal is transmitted on each spark firing. This signal communicates information by pulse width modulation.