TSB : Electronic Ignition (EI) System

Details

Used on the 2.2L, 3.0L, 3.4L, 4.2L, 4.8L, 5.3L, 6.0L and 8.1L engines, the EI system eliminates the need for a mechanical distributor. It consists of coil packs, EI modules, Crankshaft Position (CKP) sensor (2 used on 3.4L), Camshaft Position (CMP) sensor, wiring harness and the Ignition Control (IC) portion of the Powertrain Control Module (PCM). On 2.2L and 3.4L, the ignition system uses a "waste spark" method of spark distribution. Each cylinder is paired with the cylinder that is opposite it in the firing order (1-4 and 2-3), or (1-4, 2-5 and 3-6). Spark occurs simultaneously in the cylinder approaching the compression stroke and in cylinder approaching exhaust stroke. The cylinder on the exhaust stroke requires less voltage for the spark plug to fire. This leaves the bulk of the available voltage to fire the spark plug for the cylinder on the compression stroke. The process is repeated when the cylinders reverse roles. Each cylinder pair is fired by its own ignition coil. On 3.0L, 4.2L, 4.8L, 5.3L, 6.0L and 8.1L engines, ignition coils are fired sequentially and do not use the "waste spark" method. Input from the CKP sensor and EI modules is used by the PCM to control ignition timing and triggering of fuel injectors. Crankshaft Position (CKP) Sensor (2.2L 7X Signal) CKP sensor is mounted on side of engine block. CKP sensor detects position of 7 notches (7X signal) in internal crankshaft wheel. These signals are received by the EI module which allows PCM to determine ignition and fuel injector firing time. Six notches are equal distance apart (60 degrees). PCM recognizes TDC of cylinder No. 1 based on time between pulses and location of seventh notch (sync pulse) placed 10 degrees from one of the other notches. The IC module must receive 7X signal to fire the correct ignition coil. PCM uses every other notch to fire fuel injectors. The 2nd notch after the sync pulse provides a signal, triggering EI module to fire coils No. 2 and 3. Fifth notch signals coils No. 1 and 4 to fire. Crankshaft Position (CKP) Sensor (3.0L 58X Signal) CKP sensor is located underneath and slightly to the left of the oil filter housing. CKP sensor produces an AC voltage of different amplitude and frequency depending on the velocity of the crankshaft reluctor wheel. The crankshaft reluctor wheel contains 58 teeth (58X signal) that are 6 degrees apart with a 12-degree span that is uncut. This 12-degree span is used to locate the cylinder No. 1 top dead center piston position used for engine synchronization. CKP sensor in conjunction with the Camshaft Position (CMP) sensor can properly synchronize spark timing; fuel timing and spark knock control. As the reluctor wheel tooth rotates past the CKP sensor, the sensor's internal Hall Effect device pulls the signal circuit to ground. The PCM expects to one high (12 volts) to low (zero volts) transition once every 2 crankshaft rotations as the reluctor tooth passes the sensor. The signal circuit should be at 12 volts at all times except when the transition occurs. If an error occurs in the CMP sensor circuit during the drive cycle, the PCM will continue to supply fuel and spark to the correct cylinder at the correct time until the ignition is turned off. If an error occurs in the CMP sensor circuit upon key-up, the PCM 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. The large numbers of teeth on the reluctor wheel are used to correctly detect engine misfires. The PCM automatically learns the variation between all of the 58 teeth under 24 different engine speed/load ranges. To correctly detect misfires, the PCM will monitor the time it takes to pass 20 of the teeth (120 degrees of crankshaft rotation) after a cylinder has fired. If the time (based on engine speed and load) to pass the 20 teeth is too long, a cylinder misfire has occurred. Crankshaft Position (CKP) Sensor (3.4L 3X/24X Signal) Engine is equipped with 2 CKP sensors. The 3X CKP sensor is located on side of engine block. 3X CKP sensor detects position of 3 notches (3X signal) cast into crankshaft. These signals are received by the Ignition Control (IC) module which allows PCM to determine ignition and fuel injector firing time. PCM recognizes TDC of cylinder No. 1 based on "on" time between pulses and location of third notch (sync pulse) placed 10 degrees from one of the other notches. The IC module must receive 3X signal to the correct ignition coil. The 24X CKP sensor is located on a bracket at front of timing cover and produces a 24X signal used to smooth engine operation at engine speeds less than 1200 RPM. The 24X signal is generated by an interrupter ring with 24 equally spaced notches attached to rear of crankshaft balancer. Crankshaft Position (CKP) Sensor (4.2L 7X Signal) The CKP sensor is located on lower right rear of engine block. CKP sensor detects position of 7 notches (7X signal) on reluctor wheel, mounted on rear of crankshaft. The PCM uses the 7X signal (sync pulse) to synchronize the coil firing sequence with the crankshaft position. CKP sensor is connected to PCM by a signal circuit and a low reference circuit. Crankshaft Position (CKP) Sensor (4.3L, 5.0L & 5.7L 3X/4X Signal) CKP sensor is located in the front engine cover. Air gap between sensor and target wheel is preset and is not adjustable. Target wheel has 3 or 4 slots, depending on whether the engine has 6 or 8 cylinders and is keyed to the crankshaft. Rotation of target wheel creates a change in the magnetic field of the sensor which results in an induced voltage pulse. Based on these pulses, PCM is able to determine crankshaft position and engine speed. PCM will then activate the fuel injector and provide spark to distributor. Crankshaft Position (CKP) Sensor (4.8L, 5.3L, 6.0L & 8.1L 4X/24X Signal) The CKP sensor is located on lower right rear of engine block. CKP sensor detects position of 24 notches (24X signal) on reluctor wheel, mounted on rear of crankshaft. The PCM uses the 24X signal to determine when a particular cylinder is on either a firing or exhaust stroke. A 4X signal is also produced by the reluctor wheel. PCM uses the 4X signal to monitor misfires, tachometer output, spark control, fuel control and certain diagnostics. Ignition Coils (2.2L & 3.4L) On ignition coil pack, 2 or 3 separate twin tower coils, depending on whether the engine has 4 or 6 cylinders, are independently mounted over the Electronic Ignition (EI) module. Each coil provides the spark for 2 simultaneously paired spark plugs. Each coil can be replaced separately. Ignition Coils (3.0L) Each Electronic Ignition (EI) module (2 total) is located directly over each cam cover. The EI system uses a coil over plug design to eliminate the need for spark plug wires. Each El module houses 3 primary coils, 3 secondary coils as well as 3 drivers used to supply current to each of the three primary coils. Each secondary coil fires independently of the others solely based on PCM control. The PCM 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 3 primary coils. The time the PCM holds the control signal high is called the dwell time. As the PCM 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 PCM uses 3 independent control signals to fire each cylinder within that specific bank. Ignition Coils (4.2L) Six ignition coils are independently mounted above each cylinder on the rocker cover. Ignition coils are fired sequentially and are connected to the PCM by six individual Ignition Control (IC) circuits. Each coil can be replaced separately. Ignition Coils (4.8L, 5.3L & 6.0L) Eight ignition coils are independently mounted above each cylinder on the rocker covers. Ignition coils are fired sequentially and are connected to the PCM by eight individual Ignition Control (IC) circuits. Each coil can be replaced separately. Ignition Control Module (ICM) The ICM receives ignition control signals from the PCM which in turn triggers the corresponding ignition coils. Since the PCM controls spark timing and ignition control during crank and run cycles, there is no by-pass mode. ICM is not serviceable.