System Description
Ignition System Wiring.:
DESCRIPTION AND OPERATION
The SATURN distributorless ignition system (DIS) provides spark energy for air/fuel combustion in response to timing commands from the powertrain control module (PCM). System components include an electronic module with two two-tower ignition coils (module/coil pack), secondary wires and spark plugs. The SOHC (LKO) and DOHC (LLO) engines use the same module/coil pack.
DISTRIBUTORLESS IGNITION SYSTEM 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 describes 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 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.
SYSTEM OPERATION
INITIALIZATION
When the ignition switch is turned to the Run position, battery voltage (B+) is applied to the DIS module. The CPS has no output due to no engine rotation. The BYPASS line is held low by the PCM. The REF line is high. The 6X line is high. The TACH signal is low. The EST signal is held low by the DIS module. No spark occur at the spark plug until engine crank begins.
ENGINE CRANK
Crankshaft rotation initiates CPS pulses. With B+ applied to the DIS module, any valid CPS pulses shall initiate reference pulses. The BYPASS line is held low by the PCM. The system is in BYPASS mode. The REF signal and the 6X signal begin switching upon recognition of the first CPS pulse. The EST is held low by the DIS module. Spark firing events begin at TDC of the first cylinder following a recognized sync pulse. The TACH signal begins switching with the first spark firing event.
ENGINE STALL
If engine stalls, CPS pulses cease due to lack of engine rotation. Within 500 milliseconds after the last CPS pulse, any charged coils are fired. No more firing events shall occur until engine rotation resumes. The REF signal and the 6X signal stop switching and remain high. The TACH signal stops switching and remains low. The BYPASS line is pulled low by the PCM due to lack of REF pulses. The EST signal stops switching and remains low.
MODULE GROUNDING
The DIS module is grounded through Pin E of 5 Pin connector. The laminated coils have an additional, redundant ground which is provided through the bolt heads to the transaxle bell housing. The plate on the bottom of the module is used primarily for a heat sink and has no effect on module operation.
BYPASS MODE
BYPASS mode is defined as any time during engine operation that the EST signal is not controlling ignition spark timing. The BYPASS line is held low by the PCM and the EST line is held low by the DIS module. The BYPASS mode ignition timing shall be determined by the DIS module.
EST MODE
EST mode is defined as any time during engine operation that the EST signal is controlling ignition spark timing. The BYPASS line is raised by the PCM. The DIS module shall release the EST line within 5 milliseconds after the BYPASS line is raised. The PCM shall pulse the EST signal with a minimum pulse width of 1.0 millisecond. The falling edge of the EST signal defines the desired timing for the ignition event.