Ignition System: Description and Operation
DESCRIPTIONThe distributor ignition system has two distinct configurations.
Distributor Mounted ICM:
1. In the first configuration, the Ignition Control Module (ICM) is mounted on the distributor and has three pins which plug into the hall effect Camshaft Position (CMP) Sensor Profile Ignition Pickup (PIP sensor) inside the distributor. This configuration is called distributor mounted ICM.
Remote Mounted ICM:
2. The ICM on the second, remote mount ICM, is not mounted on the distributor but in another location within the engine compartment.
NOTE: Gray module indicates Push Start and black module indicates Computer Controlled Dwell (CCD).
CONSTRUCTION
The components of both configurations consist of the ICM, distributor, CMP (hall effect PIP) sensor, and E-core ignition coil.
1. The distributor used on the distributor mounted ICM configuration is called a Universal Distributor and has an opening in it through which the pins of the ICM plug into the CMP (PIP) sensor.
2. On the remote mount configuration, a Sealed Distributor is used.
The CMP (hall effect PIP) sensor is located inside the distributor on both configurations. Note also that there are no mechanisms on either distributor for centrifugal or vacuum advance.
OPERATION
The CMP (hall effect PIP) sensor inside the distributor responds to a rotating metallic shutter on the distributor shaft and produces a digital PIP signal. This signal provides base timing information and is an indication of engine speed (RPM) and position. Note that since the shutter is mounted on the distributor shaft, two revolutions of the engine crankshaft are required to fire each spark plug once. This is because the distributor rotates at half the crankshaft speed. The internal circuitry of the ICM will have one of two possible arrangements, Push Start, or Computer Controlled Dwell (CCD).
Push Start ICM Waveforms:
1. The push start system allows for increased dwell, or coil ON time, when starting the engine. The ICM on this system determines when to turn the coil ON based upon engine RPM information. The coil is then fired, or turned OFF, whenever a rising edge of a Spark Output (SPOUT) signal is encountered as shown in the Push Start ICM Waveforms image. The SPOUT signal, short for SPark OUTput, is a digital signal generated by the Powertrain Control Module (PCM) providing spark angle information to the ICM. The SPOUT signal on the push start system controls only the firing of the coil. The falling edge of the SPOUT signal is ignored.
Computer Controlled Dwell ICM Waveforms:
2. The CCD system, however, does use both edges of the SPOUT signal as shown in the Computer Controlled Dwell (CCD) ICM Waveforms image. The SPOUT signal for the CCD system is the same as in the push start except that the falling edge is now generated to control the time at which the coil is turned ON. The coil ON time, or dwell, for this system is thus entirely controlled by the SPOUT signal. The ICM does not internally determine when to turn the coil ON as it does on the push start system. It responds directly to the SPOUT signal it receives.
NOTE: In the case that the SPOUT signal line opens from the PCM, the ICM will use the PIP signal to fire the coil. This results in a fixed spark angle and fixed dwell.