The Distributorless Ignition System (DIS), also called the Electronic Ignition (EI) system, on later model vehicles, eliminates the conventional distributor and all its components, by using multiple ignition coils. Six cylinder engines use a six tower coil pack. Eight cylinder use two four tower coil packs. Each coil pack has 2 tach wires, 1 for each coil.
In the DIS ignition system, each coil fires 2 spark plugs at the same time. The plugs are paired so that the plug on the compression stroke fires, while the other plug is on its exhaust stroke. The next time the coil is fired, the plug that was on the exhaust will be on the compression and the one that was on the compression will be on the exhaust. The spark in the exhaust cylinder is wasted but little of the coil energy is lost.
The DIS ignition system consists of the following components:
These engines use a camshaft and crankshaft sensor. These sensors are hall effect devices. A rotary vane cup (or wheel), made of ferrous metal is used to trigger the hall effect devices. The camshaft cup incorporates a single tooth and is driven by the camshaft. The signal from the camshaft sensor has 1 positive-going edge once every camshaft revolution. The crankshaft cup incorporates 3 teeth and causes the crankshaft sensor to generate 3 positive (PIP) edges every crankshaft revolution.
On 1996 vehicles, there is no longer a stand-alone Ignition Control Module (ICM). The ICM has been integrated into the PCM. The Profile Ignition Pickup (PIP), Spark Output (SPOUT), Ignition Ground (IGN GND), and Ignition Diagnostic Monitor (IDM) have also been enclosed in the PCM. The functionality of the ignition remains the same.
EEC-IV Vehicles Through 1995
In the DIS ignition system the EEC-IV processor determines the spark angle using the PIP signal to establish base timing. Spout is provided by the EEC-IV processor to the DIS module and serves 2 purposes. The leading edge fires the coil and the trailing edge controls the dwell time. This feature is referred to as Computer Control Dwell (CCD).
The DIS module incorporates an Ignition Diagnostic Monitor (IDM). This is an output signal that provides diagnostic information concerning the ignition system to the EEC-IV processor for self-test. It is also the input signal for the vehicle's tachometer.
If the CID circuit fails and an attempt to start the engine is made, the DIS module will randomly select 1 of the coils to fire. If hard starting results, turning the key OFF and trying to restart will result in another guess. Several attempts may be needed until the proper coil is selected, allowing the vehicle to be started and driven until repairs can be made. The Failure Mode Effects Management (FMEM) system will try to keep the vehicle drivable despite certain EEC-IV system failures that prevent the EEC-IV processor from providing spark angle or dwell commands. The EEC-IV processor opens the SPOUT line and the DIS module fires the coils directly from the PIP input. This condition will result in a fixed spark angle of 10 degrees and a fixed dwell.
The DIS ignition module receives the PIP signal from the crankshaft sensor, the CID signals from the camshaft sensor and the Spout (spark out) signal is from the EEC-IV control module. During normal operation the PIP signal is sent to the EEC-IV control module from the crankshaft timing sensor and provides base timing and rpm information. The CID signal provides the DIS module with the information required to synchronize the ignition coils so that they are fired in the proper sequence.
When the window of the vane cup is located between the magnet and hall effect device, a magnetic flux field is completed. At this time the magnetic field is allow to travel from the permanent magnet through the hall effect device and back to the magnetic. This condition creates a low (0 volts) output signal. When the vane tooth is located between the magnet and hall effect device, the flux field is shunted through the vane and back to the magnetic. The output signal, during this time, will change from a low (0 volts) to high (source volts).1996 EEC-V Vehicles
In the EI system, the Crankshaft Position (CKP) sensor is used to indicate the crankshaft position and speed information to the PCM. By sensing a missing tooth on a trigger wheel mounted on the crankshaft damper, the CKP is also able to identify a specific point in the travel of piston 1. The PCM uses the information from the CKP sensor to generate an internal Profile Ignition Pickup (PIP) signal.
Once the PIP signal is generated, fuel and spark functions are enabled. The calculated spark target is used internally by the PCM as a pulse width modulated digital signal called the Spark Output (SPOUT). The PCM decodes the SPOUT signal and fires the next spark at the commanded spark target. The PIP signal is also used to supply a clean, inverted signal (PIP) for tachometer operation.
The PCM also serves as an electric switch for the coil primary circuit. When the switch closes, current flows and a magnetic field expands around the primary coil. When the switch opens, current flows and a magnetic field expands around the primary coil. When the switch opens, the field collapses and causes the secondary coil to fire the spark plugs at high voltage. In addition, and Ignition Diagnostic Monitor (IDM) signal is transmitted on each spark firing. This signal communicates information by pulse width modulation.
Crankshaft Timing Sensor
The crankshaft sensor, is a single hall effect magnetic device. Its provides base timing and rpm signals to by the DIS and EEC-IV modules.Camshaft Sensor
The camshaft sensor, is a single hall effect magnetic device, which is activated by a single vane driven by the camshaft. This sensor provides CID information for the ignition coil and fuel synchronization. The sensor is in the location normally used for the distributor.Ignition Coil Pack
The ignition coil pack contains six coil towers for 6-cylinder engine or two four tower coil packs for 8-cylinder engines. Each ignition coil fires 2 spark plugs simultaneously. The spark plug fired on the exhaust stroke uses very little of the ignition coil's stored energy.DIS Ignition Module
On vehicles through 1995, the DIS ignition module receives the PIP signal from the crankshaft sensor. The CID signal provides the DIS ignition module with the information required to synchronize the ignition coils so that they are fired in the proper sequence.
1996 vehicles do not have an ignition control module. The PCM determines the ignition coil ON and OFF times and calculates the desired spark angle signal.