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.

Click image to see an enlarged view

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 ignition module to fire No. 23 ignition coil and the fifth crank pulse signals the module to fire the No. 1-4 ignition coil.

During cranking, the ignition module monitors the sync-pulse to begin the ignition firing sequence and below 700 rpm the module controls spark advance by triggering each of the 2 coils at a pre-determined interval based on engine speed only. Above 700 rpm, the ECM controls the spark timing (EST) and compensates for all driving conditions. The ignition module must receive a sync-pulse and then a crank signal in that order to enable the engine to start.

To control EST the ECM uses the following inputs:

Crankshaft position
Engine speed (rpm)
Engine coolant temperature
Manifold air temperature
Engine load (manifold pressure or vacuum)

The ESC system is designed to retard spark timing up to 15 degrees to reduce spark knock in the engine. When the knock sensor detects spark knocking in the engine, it sends an A/C voltage signal to the ECM, which increases with the severity of the knock. The ECM then adjusts the EST to reduce spark knock.


Crankshaft Sensor

The crankshaft sensor, mounted remotely from the ignition module on an aluminum cover plate, is used to determine crankshaft position and engine speed.

Ignition Coil

The ignition coil assemblies are mounted inside the ignition module housing. Each coil distributes the spark for two plugs simultaneously.

Electronic Spark Timing (EST)

Reference circuit (CKT 430)-provides the ECM with rpm and crankshaft position information from the IDI module. The IDI module receives this signal from the crank sensor.
Bypass signal (CKT 424)-above 700 rpm, the ECM applies 5 volts to this circuit to switch spark timing control from the IDI module to the ECM.
EST signal (CKT 42)-reference signal is sent to the ECM via the DIS module during cranking. Under 700 rpm, the IDI module controls the ignition timing. Above 700 rpm, the ECM applies 5 volts to the bypass line to switch the timing to the ECM control.
Reference ground circuit (CKT 453)-this wire is grounded through the module and insures that the ground circuit has no voltage drop between the ignition module and the ECM which could affect performance.

ESC Sensor

The ESC sensor, mounted in the engine block near the cylinders, detects abnormal vibration (spark knock) in the engine.