GM DIS/WASTE SPARK IGNITION

SYSTEM COMPONENTS

Vehicles which are equipped with the 2.8L, 3.1L, 3.4L engines utilize the Direct Ignition System (DIS). This system is called the Electronic Ignition (EI) in later model years. This system features a distributorless ignition. The DIS/EI system consists ofthree separate coils on V6 engines, an Ignition Control Module (ICM), and a secondary conductor housing which is mounted to an aluminum cover plate. The system also consist of one or two Crankshaft Position (CKP) sensors, crankshaft reluctor ring, related connecting wires and the Electronic Spark Timing (EST) or Ignition Control (IC) portion of the Electronic Control Module (ECM). A Camshaft Position (CMP) sensor may also be incorporated on some engines.
When the term Electronic Control Module (ECM) is used in this information, it refers to the engine control computer; regardless, if the term Powertrain Control Module (PCM) or Electronic Control Module (ECM) is used.
The DIS/EI ignition system uses a magnetic crankshaft sensor (mounted remotely from the ignition module) and a reluctor to determine crankshaft position and engine speed. The reluctor is a special wheel cast into the crankshaft with several machined slots. A specific slot on the reluctor wheel is used to generate a sync-pulse.
The camshaft sensor, used on some engines, provides a cam signal to identify correct firing sequence. The crankshaft sensor signal triggers each coil at the proper time.
The ECM uses the EST circuit to control spark advance and ignition dwell, when the ignition system is operating in the EST/IC mode.
The Electronic Spark Control (ESC) system is used to control spark knock and enable maximum spark advance to improve driveability and fuel economy. This system is consists of a knock sensor and an ESC module. The computer control module (ECM/PCM) monitors the ESC signal to determine when engine detonation occurs.

SYSTEM OPERATION

The DIS or EI system uses a waste spark distribution method. Each cylinder is paired with the cylinder opposite it (1-4, 2-5, 3-6 on the V6 engines.) The ends of each coil secondary is attached to a spark plug. These 2 plugs are on companion cylinders, cylinders that are at top dead center at the same time. The one that is on compression is said to be the event cylinder and the one on the exhaust stroke, the waste cylinder. When the coil discharges, both plugs fire at the same time to complete the series circuit.
Since the polarity of the primary and the secondary windings are fixed, one plug always fires in a forward direction and the other in reverse. This is different than a conventional system firing all plugs the same direction each time. Because of the demand for additional energy; the coil design, saturation time and primary current flow are also different. This redesign of the system allows higher energy to be available from the distributorless coils, greater than 40 kilovolts at all rpm ranges.
The DIS/EI ignition system uses a magnetic crankshaft which protrudes into the engine block at approximately 0.050 inch of the crankshaft reluctor. As the crankshaft rotates, the slots of the reluctor causes a changing magnetic field at the crankshaft sensor, creating an induce voltage pulse. By counting the time between pulses, the ignition module can recognize the specified slot (sync pulse). Based on this sync pulse, the module sends reference signals to the ECM to calculate crankshaft position and engine speed.
To control EST the computer control module (ECM/PCM) uses the following inputs:

Crankshaft position
Engine Speed (rpm)
Engine temperature
Manifold air temperature
Atmospheric (barometric) pressure
Engine load (manifold pressure or vacuum)
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The ESC (Knock Sensor) system is designed to retard spark timing.