in a 95 saturn sl2 1.9 DOHC, what controls ignition spark besides the plugs, wires, coil pack, and ignition module?
What do you mean “controls?”
Are you having a problem with your Saturn? If so maybe you can give us some information. What does it do and not do? how old are the wires, plugs etc. Does the weather make a difference??
what i meant was: what tells the ignition module to send power to each individual plug. ie: the PCM?
the problem is that the engine is missing and i was able to determine that i have a very weak spark on the #3 plug, which was causing the miss since the fuel is not being completely ignited. (its not an exact test, but with each one of the spark plug wires removed in turn, the #3 wire is barely arcing between the end of the wire and the exhaust manifold where the other wires [1,2,4] are constantly arcing.) the plugs, wires, coil packs, and ignition module are all brand new. weather does not make a difference.
I am the tech manager at Autolite spark plugs. Here is how your system works. If you want specific troubleshooting instructions, contact me at firstname.lastname@example.org
Spark Plug Wire Routing.
DESCRIPTION AND OPERATION
The Saturn electronic ignition (EI) system 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.
ELECTRONIC IGNITION SYSTEM CIRCUITS
The electronic ignition (EI) system contains 11 input/output circuits and controls two, two-tower coils, each coil firing two spark plugs.
The following describes the input/output circuits of the EI module.
The BYPASS line is a five volt logic signal that indicates whether the system is in ignition control (IC) mode (five volts) or in BYPASS mode (zero volts). Either the PCM/EC or the El 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 6-0 degrees. The rising edge of REF occurs at top dead center (TDC). Before the first sync pulse is recognized, the REF will toggle on every crankshaft position sensor pulse. This feature is referred to as Quick Start
The 6X output signal is a five volt sine wave that is initially high. The signal switches low for 400 to 600 micro-seconds at each of the six, sixty degree CKP 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
Ignition Control (IC) signal is a five volt square wave supplied by the PCM. In EST mode, the falling edge of the IC signal defines the desired spark timing. In BYPASS mode, the IC line is held low by the EI module.
REFERENCE LOW (REF LO) LINE
The reference low (REF LO) output signal is a low current ground reference supplied by the EI 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.
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.
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 (CKP) sensor 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 CKP signal defines engine position. A CKP 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 CKP 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.
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 El module. The CKP 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 IC signal is held low by the EI module. No spark occur at the spark plug until engine crank begins.
Crankshaft rotation initiates CKP pulses. With B+ applied to the EI module, any valid CKP pulses will 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 CKP pulse. The IC signal is held low by the EI 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.
If engine stalls, CKP pulses stop due to lack of engine rotation. Within 500 milliseconds after the last CKP pulse, any charged coils are fired. No more firing events will 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 IC signal stops switching and remains low.
BYPASS mode is defined as any time during engine operation that the IC signal is not controlling ignition spark timing. The BYPASS line is held low by the PCM and the IC line is held low by the El module. The BYPASS mode ignition timing will be determined by the EI module.
IC (EST) MODE
Ignition control mode is defined as any time during engine operation that the IC signal is controlling ignition spark timing. The BYPASS line is raised by the PCM. The EI module will release the EST line within 5 milliseconds after the BYPASS line is raised. The PCM will pulse the IC signal with a minimum pulse width of 1.0 millisecond. The falling edge of the IC signal defines the desired timing for the ignition event.
The EI 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.
The electronic ignition module accepts ignition timing information from the PCM and engine position information from a crankshaft position (CKP) sensor. 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.
The secondary wires transmit the high voltage energy from the coil secondaries to the spark plugs.
The spark plugs allow the high voltage energy from the coils to arc across a gap to ignite the air/fuel mixture.
Thanks motorking! i really appreciate that information. with the included specified voltages ill be able to narrow down whats causing my problem, but based on what you just gave me, i am even more inclined to believe that my PCM has developed a problem, since all feeds and controls originate there. there are several nearby junkyards, so as soon as i go off of my current work week im going to pick up a PCM and see how it goes. thanks again motorking!