GM Lumina/Grand Prix/Cutlass Supreme/Regal 1988-1996

General Description


See Figure 1

Vehicles with the 2.3L engine are equipped with the Integrated Direct Ignition (IDI) system. This system features a distributorless ignition. The IDI system consists of two separate ignition coils, an ignition module and a secondary conductor housing mounted to an aluminum cover plate. The system also consists of a crankshaft sensor, connecting wires and the Electronic Spark Timing (EST) portion of the Electronic Control Module (ECM).

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 IDI 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 7 slots machined into it. Six of the slots are equally spaced 60 degrees apart and the seventh slot is spaced 10 degrees from 1 of the other slots. This seventh slot is used to generate a sync-pulse.

The ECM uses the EST circuit to control spark advance and ignition dwell, when the ignition system is operating in the EST mode.

To control spark knock and to use maximum spark advance to improve driveability and fuel economy, an Electronic Spark Control (ESC) system is used. This system consists of a knock sensor and an ESC module. The ECM monitors the ESC signal to determine when engine detonation occurs.

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Fig. Fig. 1: Exploded view of the IDI system components


The Integrated Direct Ignition (IDI) system uses a waste spark distribution method. Each cylinder is paired with the cylinder opposite it (i.e. 1-4, 2-3). 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 IDI ignition system uses a magnetic crankshaft sensor mounted remotely from the ignition module. It protrudes into the block at approximately 0.050 inch (1.3mm) of the crankshaft reluctor. As the crankshaft rotates, the slots of the reluctor cause a changing magnetic field at the crankshaft sensor, creating an induce voltage pulse.

The IDI module sends a reference signal to the ECM, based on the crankshaft sensor pulses, which are used to determine crankshaft position and engine speed. Reference pulses to the ECM occurs at a rate of 1 per each 180 degrees of crankshaft rotation. This signal is called the 2X reference because it occurs 2 times per crankshaft revolution.

A second reference signal is sent to the ECM which occurs at the same time as the sync-pulse, from the crankshaft sensor. This signal is called the 1X reference because it occurs 1 time per crankshaft revolution.

By comparing the time between the 1X and 2X reference pulses, the ignition module can recognize the sync-pulse (the seventh slot) which starts the calculation of the ignition coil sequencing. The second crank pulse following the sync-pulse signals the