Spark Control System
The PCM is responsible for maintaining proper spark and fuel injection timing for all driving conditions. To provide optimum driveability and emissions, the PCM monitors input signals from the following components in calculating Ignition Control (IC) spark timing:^ Ignitions Control module (ICM).
^ Engine Coolant Temperature (ECT) sensor.
^ Intake Air Temperature (IAT) sensor.
^ Mass Air Flow (MAF) sensor.
^ Trans Range inputs from Transaxle Range switch.
^ Throttle Position (TP) sensor.
Vehicle Speed Sensor (VSS).
CIRCUITS AFFECTING IGNITION CONTROL
To properly control ignition timing, the PCM relies on the following information:
^ Engine load (manifold pressure or vacuum)
^ Atmospheric (barometric) pressure
^ Engine temperature
^ Intake air temperature
^ Crankshaft position
^ Engine speed (RPM)
The Ignition Control (IC) system consists of the following components:
^ Ignition coils
^ Ignition control module
^ 7x crankshaft position sensor
^ 24X crankshaft position sensor
^ Powertrain control module
^ All connecting wires
The electronic Ignition Control Module (ICM) connector terminals are identified as shown in the Electronic Ignition System graphic. These circuits perform the following functions:
^ 3X reference high (CKT 430) - The 7x crankshaft position sensor sends a signal to the electronic ignition control module which generates a reference pulse that is sent to the PCM. The PCM uses this signal to calculate crankshaft position and engine speed (also used to trigger the fuel injectors).
^ 3X reference low (CKT 453) - This wire is grounded through the ICM and assures the ground circuit has no voltage drop between the ICM and the PCM.
^ Ignition control bypass (CKT 424) - During initial cranking,the PCM will look for synchronizing pulses from the camshaft position sensor and the 7x crankshaft position sensor. The pulses indicate the position of the #1 piston and the #1 intake valve. Five volts is applied to the bypass circuit at precisely the same time these signals are received by the PCM. This generally occurs within one or two revolutions of the crankshaft. An open or grounded bypass circuit will set a DTC P135O and the engine will run at base ignition timing. A small amount of spark advance is built into the ignition control module to enhance performance.
^ Ignition Control (IC) (CKT 423) - The PCM uses this circuit to trigger the electronic ignition control module. The PCM uses the crankshaft reference signal to calculate the amount of spark advance needed.
^ 24X reference signal - The 24X crankshaft position sensor increases idle quality and low speed driveability by providing better resolution at a calibrated RPM.