Ignition Control Module: Description and Operation

Ignition Module/Coil Assembly.:

Ignition Module With Coils.:

The ignition module/coil pack are bolted together as an assembly, but may be disassembled for service of the individual coils or module.


TIMING CONTROL
The electronic module accepts ignition timing information from the PCM and engine position information from a crankshaft position sensor (CPS). It charges up the appropriate ignition coil to a preset current limit then turns "OFF" the primary current at the desired engine position to create a high voltage signal that is routed to the spark plug to ignite the air/fuel mixture.

DISTRIBUTORLESS IGNITION MODULE CIRCUITS
The distributorless ignition system (DIS) contains 11 input/output circuits and controls two-tower coils, each coil firing two spark plugs each. The following are the input/output circuits of the DIS module.


Bypass Line
The BYPASS line is a five volt logic signal that indicates whether the system is in electronic spark timing (EST) mode (five volts) or in BYPASS mode (zero volts). Either the PCM/EC or the DIS module can pull the BYPASS line low (zero volts). Only the PCM/EC can raise this line (five volts).

Reference (REF) Line
The reference (REF) output signal is a five volt square wave that is initially high. It is used by the PCM to determine engine position and engine RPM. After the first sync pulse is recognized, the REF signal is high for 120 degrees then low for 60 degrees. The rising edge of REF occurs at top dead center (TDC). Before the first sync pulse is recognized, the REF shall toggle "ON" every crankshaft position sensor (CPS) pulse. This feature is referred to as Quick Start.

6X Line
The 6X output signal is a five volt square wave that is initially high. The signal switches low for 400 to 600 micro-seconds at each of the six, sixty degree CPS pulses. The 6X signal does not switch low at the sync pulse and is fed to the ECM for possible resolution enhancement during low RPM operation and/or knock control windowing.

Electronic Spark Timing (EST) Line
The electronic spark timing (EST) signal is a five volt square wave supplied by the PCM. In EST mode, the failing edge of EST defines the desired spark timing. In BYPASS mode, the EST line is held low by the DIS module.

Reference Low (REF LO) Line
The reference low (REF LO.) output signal is a low current ground reference supplied by the DIS module to the PCM.

Buffered Tach Line
The TACH output signal is a five volt square wave that is initially low. The tach signal goes high twice per revolution. The signal shall be identical to REF after sync-up. Minimum low time shall be equivalent to 60 degrees of crankshaft rotation.

Power Input
The power input (B+) is tied to the positive terminal of the battery (12 volts nominal) and is fed through the ignition switch and inline fuse.

Power Ground
The power ground connection is a high current (7-9 AMP) connection tied to the negative terminal of the battery.

Crankshaft Position Sensor-Positive
The crankshaft position sensor (CPS) positive line is tied to the positive connection of the polarized variable reluctance crankshaft position sensor. The peak positive voltage depends on engine rpm, and ranges from 300 millivolts to 125 volts.

The CPS signal defines engine position. A CPS pulse occurs at each TDC, at 60 degrees after top dead center, (ATDC) and at 120 degrees ATDC. A seventh pulse, referred to as the sync pulse, occurs at 70 degrees ATDC of cylinder # 1.

Crankshaft Position Sensor-Negative
The CPS negative Line is tied to the negative connection of the polarized variable reluctance crankshaft position sensor. The peak negative voltage depends on engine rpm and ranges from -250 millivolts to -120 volts.



SECONDARY COIL TOWERS
The secondary signal is a high voltage (up to 40,000 volts) timed signal, routed by way of the secondary wires to the spark plugs.