Electronic Ignition System

The Electronic Ignition (EI) module, ignition coil housing with coil packs and spark plug boots are bolted as an assembly to the top of cam cover. The EI module charges and discharges the coils based on ECM control. The ECM uses a high control signal of about 5 volts to charge up the coil and a low control signal of about zero volts to discharge the coil. If coil is charged and the control signal is low, the coil will fire through its secondary towers. ECM controls spark timing and dwell (spark on-time) under all engine running conditions.

• Camshaft Position Sensor
  
  The Camshaft Position (CMP) sensor is a Hall Effect switching device used to determine the position of the bank 2 exhaust camshaft. The CMP sensor detects a single tooth on the reluctor wheel of the camshaft, which denotes 90 degrees before top dead center cylinder No. 1 compression stroke. The sensor is used by the ECM to determine when cylinder No. 1 is approaching top dead center necessary to synchronize the correct firing order. The CMP sensor is also used to enable sequential or independent fuel injection and to enable spark knock control.

  As the reluctor wheel tooth rotates past the sensor, the sensors internal hall effect device pulls the signal circuit to ground. Therefore, the ECM expects to see one high (5 volts) to low (0 volts) voltage transition once every 2 crankshaft rotations as the reluctor tooth passes the sensor. The signal circuit should be at 5 volts at all times except when the transition occurs. If an error occurs in the CMP sensor circuit during the drive cycle, the ECM will continue to supply fuel and spark to the correct cylinder at the correct time until the ignition switch is turned to OFF position. If an error occurs in the CMP sensor circuit upon key-up, then the engine is started, the ECM will default to supplying spark to both mating cylinders and enter non-sequential fuel injection. The engine may experience a 2-3 second extended crank, however, the engine will start and run.

• Crankshaft Position Sensor
  
  The Crankshaft Position (CKP) sensor circuits consist of a signal circuit, a low reference circuit and a ground circuit. The ground wire is shielded to prevent electromagnetic interference in the CKP sensor circuits. The CKP sensor is a permanent magnet generator known as a variable reluctance sensor. The CKP sensor produces an AC voltage of varying amplitude and frequency. Frequency depends on the velocity of the crankshaft. AC voltage output depends on crankshaft position and battery voltage. The CKP sensor works in conjunction with a 58-tooth reluctor wheel attached to the crankshaft. As each reluctor wheel tooth rotates past the CKP sensor, the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The sensor returns a digital ON/OFF pulse 58 times per crankshaft revolution. The ECM processes the pulses to create a signature pattern that enables the ECM to determine the crankshaft position. The ECM can synchronize the ignition timing, the fuel injector timing, and the spark knock control based on the CKP sensor and CMP sensor inputs. The CKP sensor is also used to detect misfire and tachometer display. The ECM learns the variations between all of the 58 teeth under different speed and load conditions to correctly detect misfires. The CKP sensor is located on engine block, near oil filter housing. See Fig 1 .
  Fig 1: Locating Crankshaft Position Sensor

  Courtesy of GENERAL MOTORS CORP.
• Crankshaft Reluctor Wheel
  
  The crankshaft reluctor wheel is part of the crankshaft. The reluctor wheel consists of 58 teeth and a reference gap. Each tooth on the reluctor wheel is spaced 6 degrees apart with a 12-degree space for the reference gap. The pulse from the reference gap is known as the sync pulse. The sync pulse is used to synchronize the coil firing sequence with the crankshaft position, while the other teeth provide cylinder location during a revolution. The reference gap enables the ECM to determine top dead center for cylinder No. 1 and its mating cylinder, cylinder No. 4.
• Ignition Coil
  
  Each Electronic Ignition (EI) module is located directly over the cam cover. The EI system uses a coil over plug design to eliminate the need for spark plug wires. The El module houses the primary coils, secondary coils as well as drivers used to supply current to each of the primary coils. Each secondary coil fires independently of the others solely based on ECM control. The ECM sends a low current 5-volt control signal, which turns on a driver internal to the El module, allowing current to flow to one of the primary coils. The time the ECM holds the control signal high is called the dwell time. As the ECM turns off the control signal, the secondary coil will fire out of its secondary tower. The spark will travel down the spark plug boot, across the spark plug gap to ignite the cylinder air/fuel charge. The ECM uses independent control signals to fire each cylinder within that specific bank.
• Ignition Control Module
  
  Each Ignition Coil Module (ICM) has the an ignition voltage circuit, a ground circuit and 3 control circuits, one for each ignition coil. The ECM can command each ignition coil ON by grounding the control circuit of the ignition coil. The control circuit is pulse width modulated ON/OFF in order to precisely control the spark event. The spark plugs are connected to each coil by a short boot. The boot contains a spring that conducts the spark energy from the coil to the spark plug. The spark plugs are tipped with platinum for long wear and higher efficiency.