EXCEPT 3.5L (VIN H) ENGINE
The Electronic Ignition (EI) systems used on the 3.1L (VIN M), 3.4L (VIN X and VIN E) and 3.8L (VIN K and VIN 1) engines use a coil pack with one ignition coil for each two cylinders in the engine. Mounted under the ignition coils on each system is an Ignition Control Module (ICM) that performs the ignition coil switching functions and interacts with the Powertrain Control Module (PCM) to optimize ignition system operation.
On these engine systems, the spark timing is controlled electronically. The ICM controls the spark timing during engine start up, and provides a back up timing system that will allow the engine to run in the event of an open or ground in the Ignition Control (IC) circuit. Once the engine starts and is running above the approximate engine speed of 400 RPM, the PCM takes over the spark timing and sends signals to the ICM for ignition coil switching.
The electronic ignition system used on most of these engines uses a "waste spark" method of spark distribution. Each cylinder is paired with its opposing cylinder in the firing order, so that one cylinder on compression fires simultaneously with the opposing cylinder on exhaust. The spark that occurs in the cylinder that is on the exhaust stroke is referred to as the "waste spark".
The spark plugs in the two opposing cylinders are connected to the two secondary terminals of the same ignition coil. The spark voltage appears at the center electrode of one of the spark plugs and jumps to the side electrode, then passes through the engine to the other spark plug. At the second spark plug, the spark jumps from the side electrode to the center electrode and completes the series circuit back to the ignition coil. The high level of energy available from the ignition coil is more than sufficient to fire both plugs simultaneously. Since the waste spark requires very little of the available voltage to fire, most of the coil output voltage is available to fire the cylinder that is on the compression stroke.
Engine speed (RPM) and cylinder position in the intake-compression-power-exhaust sequence are sensed electronically and are used by the ICM and PCM to control timing. A magnetic Crankshaft Position (CKP) sensor mounted in the engine block provides these parameters. The magnetic CKP sensor consists of a wire coil wound around a permanent magnet. The sensor is positioned near a reluctor ring on the crankshaft. The reluctor ring has notches, which trigger signals in the magnetic sensor to indicate Crankshaft Position (CKP), and crankshaft speed (RPM). These signals are used by the ICM during start up, then passed on to the PCM to help determine optimum timing while the engine is running. The PCM also uses other inputs separate from the ignition system itself, to determine optimum timing. More information is available in , Electronic Engine Controls.
The 3.8L engines use a dual Crankshaft Position (CKP) sensor to monitor engine speed and stroke sequence. It is mounted on the engine beside the harmonic balancer/crankshaft pulley. The sensor has dual Hall-Effect switches that sense interrupter rings on the harmonic balancer. Gaps in the interrupter rings cause signals to be generated by the sensor to indicate crankshaft position and speed (RPM). These signals are sent to the ICM for use during start up, then on to the PCM for use in timing as the engine runs. The PCM also uses other inputs separate from the ignition system itself, to determine optimum timing. The 3.4L (VIN E) engine uses a 7X Crankshaft Position (CKP) sensor that reads off a toothed portion of the crankshaft and a 24X CKP sensor that reads off the crankshaft pulley
The 3.8L engines also use a Camshaft Position (CMP) sensor which is mounted on the front engine cover above the crankshaft balancer and below the coolant pump. The signal from this sensor passes through the ICM to the PCM, and is used for fuel synchronization.
3.5L (VIN H) ENGINE
The Electronic Ignition (EI) system on the 3.5L (VIN H) engine used in the 2000 Intrigue is different from the other V6 applications covered by this guide. The ignition system on this engine uses an individual ignition coil for each cylinder. An ignition coil assembly consisting of three coils and an ignition control module, is located in the center of each cam cover. This arrangement allows the ignition coil to connect directly to the spark plug using only a boot. This eliminates the need for secondary spark plug wires. There are separate ignition modules for Bank 1 and Bank 2. Each module controls the three ignition coils for that bank of cylinders. The PCM controls ignition module operation. There are six Ignition Control (IC) units, one per cylinder, that connect the PCM and the ignition modules. The ignition modules also have a power feed, a chassis ground circuit and a Reference Low circuit each. The PCM causes spark to occur by pulsing the IC circuit, which signals the ignition module to trigger the ignition coil and fire the spark plug. Sequencing and timing are PCM controlled. The ignition feed circuits are fused separately for each bank of the engine. The two fuses also supply the injectors for that bank of the engine. This system puts out very high ignition energy for plug firing. Because there are no ignition wires, there is no energy loss due to ignition wire resistance. Also, since the firing is sequential, each coil has five events to saturate as opposed to the two in a waste spark arrangement. Furthermore, no energy is lost to the resistance of a waste spark system. The ignition timing on this engine is not adjustable and, in fact, there are no timing marks on the crankshaft pulley.
The Crankshaft Position (CKP) sensor on the 3.5L (VIN H) engine is actually two sensors in a single housing. Each sensor has a separate power, ground and signal circuit. The Powertrain Control Module (PCM) supplies 12 volts to both sensors. The PCM provides the ground path, or sensor return circuit, from both sensors. These power and ground circuits are also connected to the Camshaft Position sensor. Two separate signal circuits connect the CKP sensor and the PCM. The PCM can use three different modes of decoding crankshaft position. During normal operation, the PCM performs an Angle Based calculation using both signals to determine crankshaft position. The dual sensor allows the engine to run even if one signal is lost. If either signal is lost, the PCM switches to a Time Based method of calculating crankshaft position. If the system is operating in Time A mode, the PCM is using only the signal from Sensor A. Time B indicates that the Sensor B signal is being used. If the lost signal is restored, the PCM will continue to operate in Time Based mode for the remainder of the current key cycle. The PCM will revert back to the Angle mode on the next start if the fault is no longer present. A scan tool can display the Crank Position Sensing Decode Mode and any fault-based Diagnostic Trouble Codes. The CKP sensor is considered the most critical part of the ignition system. If the sensor is damaged so that pulses are not generated, the engine will not start. In addition, CKP sensor clearance is very important. Excessive clearance can result from improper installation, dirt/debris or the old O-ring left in the block cavity when a new sensor is installed. Insufficient clearance will damage the sensor. The sensor must not contact the rotating crankshaft reluctor wheel at any time. The reluctor wheel is cast integrally with the crankshaft. Sensor to reluctor wheel clearance is not adjustable.
The Camshaft Position (CMP) sensor on the 3.5L (VIN H) engine produces a signal, which, when combined with the CKP sensor signal, enables the PCM to determine exactly which cylinder is on a firing stroke. The PCM can then properly synchronize the ignition system, fuel injectors and knock control. The CMP sensor has a power, ground and signal circuit. The PCM supplies 12 volts to the sensor. The PCM provides the ground path, or sensor return circuit, from the sensor. These power and ground circuits are also connected to the CKP sensor. If a problem is detected with the CMP circuit. A Diagnostic Trouble Code will be set that can be read by a scan tool.
IGNITION SYSTEM PRECAUTIONS
There are important considerations to point out when working around the ignition system.