Electronic Ignition (EI) System Description
The Ignition Control System for this Powertrain controls fuel combustion by providing a spark to ignite the compressed air/fuel mixture in each cylinder at the correct time. The ignition control system has several advantages over a mechanical distributor ignition system.
- No moving parts to wear out.
- No mechanical load on the engine.
- Elimination of mechanical timing adjustments.
- Located for easier service and improved reliability.
- Improved high engine speed performance.
The Ignition Control System consists of the following components:
- Two crankshaft position sensors (A and B).
- Crankshaft reluctor ring.
- Camshaft position sensor.
- Ignition control module.
- 4 separate ignition coils.
- Eight spark plug wires and conduit.
- Eight spark plugs.
- Knock sensor.
- Powertrain Control Module (PCM).
System Operation
The Ignition Control System does not use a conventional distributor or a single ignition coil. In this ignition system, both ends of each of the four ignition coils are connected to a spark plug. Each coil is connected with spark plugs on companion cylinders, i.e., on top dead center at the same time (1-4, 2-5, 6-7, and 3-8). One cylinder is on its compression stroke when the other one is on its exhaust stroke.
When the coil discharges, both plugs fire at the same time by using the engine block to complete the electrical circuit. The cylinder on the compression stroke is called the event cylinder and the one on the exhaust stroke is the waste cylinder. The two cylinders share the energy available from the ignition coil to fire both spark plugs. This method of ignition is called waste spark ignition.
Since the polarity of the ignition coil primary and secondary windings does not change, one spark plug always fires with a forward current (center electrode to ground electrode) and its companion plug fires with a reverse current (ground electrode to center electrode). This is different from a conventional distributor ignition system that fires all the plugs with the same forward current flow.
It is possible for one spark plug to fire even though a plug wire from the same coil may be disconnected from its companion spark plug. The disconnected plug wire acts as one plate of a capacitor and the engine block acts as the other plate. These two capacitor plates are charged as a spark first jumps across the gap of the connected spark plug. The plates are then discharged as the energy is dissipated as the spark continues. Voltage requirements are very high with an open spark plug or wire. The ignition coil may have enough reserve energy to fire the connected plug at idle, but possibly not under some engine load conditions. A more noticeable misfire may be evident under load; both spark plugs may then not fire.
Crankshaft Position Sensors and Reluctor Ring
The two crankshaft sensors are located on the front bank (BANK 2) of the engine block between cylinders 4 and 6. Crankshaft position A sensor is located in the upper crankcase and crankshaft position B sensor is located in the lower crankcase. Both sensors extend into the crankcase and are sealed to the engine block with O-rings. The crankshaft position sensors are not adjustable.
The magnetic crankshaft position sensors operate similar to the pickup coil in a distributor. When a piece of steel (called a reluctor) is repeatedly moved over the sensor, a voltage will be created by the sensor that appears to go On-Off-On-Off-On-Off. This On-Off signal is also similar to the signal that a set of breaker points in a distributor would generate as the distributor shaft turned and the points opened and closed.
The reluctor ring is cast onto the crankshaft between the #3 and #4 main bearing journals. The reluctor ring has 24 evenly spaced notches or air gaps and an additional 8 unevenly spaced notches for a total of 32.
As the crankshaft makes one complete revolution, both the A and B sensors will produce 32 On-Off pulses per revolution. In addition, the A sensor is positioned 27 degrees of crankshaft revolution before the B sensor. This creates a unique pattern of On-Off pulses sent to the ignition control module so that it can recognize crankshaft position.
Camshaft Sensor
The camshaft position sensor is located on the rear cylinder bank (BANK 1) in front of the exhaust camshaft. The camshaft position sensor extends into the rear cylinder head and is sealed with an O-ring. The camshaft position sensor is not adjustable.
As the rear cylinder bank exhaust camshaft turns, a steel pin on its drive sprocket passes over the magnetic camshaft position sensor. This creates an On-Off-On-Off signal sent to the ignition control module similar to the crankshaft position sensors. The camshaft position sensor produces one On-Off pulse for every one revolution of the camshaft or every two revolutions of the crankshaft. This allows the ignition control module to recognize camshaft position.
Ignition Control Module
The Ignition Control (IC) module is located on top of the rear camshaft cover. The IC module performs several functions:
- It monitors the On-Off pulses produced by the two crankshaft and one camshaft position sensors.
- It creates a 4X and 24X reference signal (4X REF HI and 24X Crank) sent to the PCM for ignition control.
- It creates a camshaft reference signal (CAM HI) sent to the PCM for fuel injection control.
- It provides a ground reference (REF LO, CAM LO) to the PCM.
- It provides a means for the PCM to control spark advance (BYPASS and IGNITION CONTROL) called IGNITION CONTROL MODE.
- It provides a limited means of controlling spark advance without PCM input called MODULE MODE.
- The IC module is not repairable. When a module is replaced the remaining components must be transferred to the new module.
Ignition Coils
Four separate coils are mounted to the module assembly. Each coil provides the spark for two spark plugs simultaneously (wasted spark ignition). Each coil can be replaced separately.
Base Ignition Timing
The base ignition timing is determined by the relationship of the crankshaft position sensors to the reluctor ring. This relationship is not adjustable and results in a base ignition timing of 10 degrees BTDC.
IC Module Mode
There are two modes of ignition system operation: PCM mode and Ignition Control Module (IC Module) mode. In IC Module mode, the ignition system operates independently from the PCM. The ignition control module maintains a base ignition timing of 10 degrees BTDC and is able to change this ignition timing slightly with increased engine speed. IC Module mode is in effect whenever an ignition control fault is detected while the engine is running and it will have a noticeable effect on driveability. In PCM mode, the PCM controls the ignition timing. The PCM calculates the desired ignition timing based on information it receives from the input sensors.
PCM Timing Mode
The Powertrain Control Module (PCM) controls spark advance and fuel injection for all driving conditions. The PCM monitors input signals from the following components as part of its ignition control function to determine the required ignition timing:
- Ignition Control Module (IC Module).
- Engine Coolant Temperature (ECT) sensor.
- Manifold Absolute Pressure (MAP) sensor.
- Transaxle Range (TR) switch.
- Throttle Position (TP) sensor.
- Vehicle Speed Sensor (VSS).
- Knock Sensor (KS).
- The crankshaft reluctor ring has 24 evenly spaced notches plus 8 additional notches (shaded) used for synchronization.
- As the crankshaft rotates, the notches pass the position sensors and create a voltage pulse signal in the sensor that is an input for the ignition control module (ICM).
- Because of the physical location of the 2 crankshaft position sensors, the signal of B lags the signal of A by 27 degrees of crankshaft revolution.
- To synchronize the ignition, the ICM first counts the number of B pulses between every 2 A pulses. There can be 0, 1, or 2 B pulses between A pulses.
- When the ICM sees 0 B pulses between A pulses , it starts counting B pulses between A pulses. When the ICM counts exactly 4, it synchronizes the ignition on the very next A pulse. If the ICM counts over 4 (jumps from 3 to 5), it waits for another B pulse between A pulse to start counting again.
- This process allows the ignition to synchronize and fire the first spark plug within 180 degrees (1/2 engine revolution).
- The camshaft position (CMP) sensor provides the ICM with cylinder #1 firing order information, which the PCM uses for sequential fuel injection.
- Using 3 sensors allows the ICM to maintain ignition synchronization even if one of the 3 sensors fails.
Ignition Control Module Inputs and Outputs