Ignition System: Description and Operation
24X Crankshaft Sensor Installation:
Crankshaft Position Sensor Installation:
Camshaft Sensor:
Crankshaft And Camshaft Sensor Wiring:
Injector And Ignition Wiring:
CIRCUIT DESCRIPTION
The Electronic Ignition (EI) system uses a waste spark method of spark distribution. In this type of ignition system, the electronic ignition control module triggers the #1/4 coil pair resulting in both #1 and #4 spark plugs firing at the same time. #1 cylinder is on the compression stroke at the same time #4 is on the exhaust stroke, resulting in a lower energy requirement to fire #4 spark plug. This leaves the remainder of the high voltage to be used to fire #1 spark plug. On this application, the crank sensor is mounted to the engine block and protrudes through the block to within approximately .050" of the crankshaft reluctor. Since the reluctor is a machined portion of the crankshaft and the crankshaft position sensor is mounted in a fixed position on the block, timing adjustments are not possible or necessary.
GENERAL DESCRIPTION
The Electronic Ignition (EI) system consists of a camshaft sensor, a crankshaft sensor, a dual hall-effect crankshaft position sensor, an engine crankshaft balancer with crankshaft position sensor interrupter rings attached to the rear, the Ignition Control (IC) portion of the PCM, The Knock Sensor (KS) control portion of the PCM, an ignition control module, three ignition coils, and the related connecting wires.
CAMSHAFT SENSOR
The camshaft sensor sends a signal to the PCM which uses it as a "sync pulse" to trigger the injectors in proper sequence. The cam signal is passed through the ignition module to the PCM for control of Sequential Fuel Injection.
3X CRANKSHAFT SENSOR
The 3X crankshaft sensor is hall-effect sensor mounted on the side of the engine block. This sensor protrudes into the block, within approximately .050" of the engine crankshaft reluctor wheel. The reluctor is a special wheel cast into the crankshaft with seven slots machined into it, six of which are evenly spaced 60° apart. A seventh slot is spaced 10° from one of the other slots and serves to generate a "sync pulse," indicating the exact position of the crankshaft once each revolution. As the crankshaft rotates, the slots in the reluctor wheel cause changes in the magnetic field of the sensor, turning the switch "OFF" and "ON" to produce a pulse that is easily measured.
By measuring the time between pulses, the DIS module can recognize the pulse representing the seventh slot or "sync pulse." Based on this "sync pulse," the DIS module sends a reference signal to the PCM to calculate crankshaft position (used to fire the ignition coils in correct sequence) and engine speed.
24X CRANKSHAFT SENSOR
The ignition control module interprets the 24X and 3X "ON-OFF" signals as an indication of crankshaft position, and must have both signals to "fire" the correct ignition coil. Since the 3X interrupter gaps in the harmonic balance each have a different width (10°, 20°, & 30°), the PCM can tell the difference between the three 3X signals. Correct ignition coil firing sequence is determined based on how many 24X signals occurs during the 3X signal.
KNOCK SENSOR
The knock sensor (KS) signal (CKT 496) goes directly to the PCM and is used by the PCM in its determination of Ignition Control (IC) during periods of detected ignition knock. When the knocking stops, the PCM advances timing in small increments. This allows the PCM to maintain maximum timing advance under various conditions.
Ignition Current Flow:
COIL OPERATION
Three separate coils are mounted to the module assembly. Each coil provides the spark for two plugs simultaneously. Each coil can also be replaced separately. A "Waste Spark" method of distribution is used on this system. Each cylinder is paired with its opposing cylinder in firing order so that one cylinder on the compression stroke fires simultaneously with its opposing cylinder on the exhaust stroke. Requiring less voltage to fire the plug on the exhaust stroke, most of the available voltage is sent to the compression stroke cylinder. This process is reversed as the cylinders' roles are reversed.
CIRCUITS AFFECTING IGNITION CONTROL
To properly control timing, the PCM relies on the following information:
^ Engine load (MAP)
^ Atmospheric pressure
^ Engine temperature
^ Intake air temperature
^ Crankshaft position
^ Engine speed
These circuits perform the following functions:
3X Reference High (CKT 430) - The crankshaft position sensor sends a signal to the electronic ignition control module which generates a reference pulse which is sent to the PCM. The PCM uses this signal to calculate crankshaft position and engine speed (also used to trigger the injector).
3X Reference Low (CKT 453) - This wire is grounded through the module and makes sure the ground circuit has no voltage drop between the ignition module and the PCM, which if open, could affect performance.
Ignition Control Bypass (CKT 424) - During initial cranking, the PCM will look for synchronizing pulses from the camshaft and 3X crankshaft position sensor indicating the position of #1 piston and intake valve. Five volts is applied to the bypass circuit the instant these signals are received by the PCM. This generally occurs within 1 or 2 revolutions of the crankshaft. An open or grounded bypass circuit will set a DTC 42 and the engine will run at base timing. A small amount of advance is built into the ignition control module to enhance performance.
IC (CKT 423) - The PCM uses this circuit to trigger the electronic ignition control module.The PCM uses the crankshaft reference signal to base its calculation of the amount of spark advance needed under present engine conditions.
24X Reference Signal - Additional to the electronic ignition system is the 24X crankshaft position sensor. Its function is to increase idle quality and provide good low speed driveability.