GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

General Information

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See Figure 1

All vehicles with the 2.3L (VIN A, D, and 3) and 2.4L (VIN T) engines are equipped with the Integrated Direct Ignition (IDI) or Electronic Ignition (EI) system, depending on the year of your vehicle. These systems feature distributorless ignition. The IDI or EI system consists of two separate ignition coils, an ignition module/Ignition Control Module (ICM) and a secondary conductor housing which is mounted to an aluminum cover plate. The system also consists of a Crankshaft Position (CKP) sensor, related connecting wires and the Electronic Spark Timing (EST) or Ignition Control (IC) portion of the computer control module (ECM or PCM depending upon vehicle year).

The IDI/EI 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° apart and the seventh slot is spaced 10° from 1 of the other slots. This seventh slot is used to generate a sync-pulse.

The IDI/EI system uses the same Electronic Spark Timing (EST) or Ignition Control (IC) circuits as the distributor-type ignition. The computer control module (ECM/PCM) uses the EST/IC 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 consists of a knock sensor and an ESC module (part of Mem-Cal). The computer control module (ECM/PCM) monitors the ESC signal to determine when engine detonation occurs.

The IDI or EI system uses a waste spark distribution method. Each cylinder is paired with the cylinder opposite it (1-4, 2-3). The end of each coil secondary is attached to a spark plug. These two plugs are on companion cylinders, meaning they 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 differs from a conventional system in which all plugs fire in 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 or EI system uses a magnetic crankshaft sensor mounted remotely from the Ignition Control Module (ICM). It protrudes into the block to within approximately 0.050 in. (1.3mm) of the crankshaft reluctor. The reluctor is a special wheel cast into the crankshaft with seven slots machined into it. Six of the slots are equally spaced (60° apart) and the seventh slot is spaced 10° from one of the other slots and serves to generate a "sync-pulse". As the crankshaft rotates, the slots of the reluctor cause a changing magnetic field at the crankshaft sensor, creating an induced voltage pulse.

The ICM or ignition module sends reference signals to the computer control module (ECM/PCM), based on the Crankshaft Position (CKP) sensor pulses, which are used to determine crankshaft position and engine speed. Reference pulses to the computer control module occur at a rate of 1 per each 180° of crankshaft rotation for vehicles through 1992, or 7 per 360° of crankshaft rotation for 1993-98 vehicles. This signal is called the 2X or 7X reference because it occurs 2 or 7 times per crankshaft revolution, depending on the year of your vehicle.

For 1993-98 vehicles, the 7X reference signal is necessary for the PCM to determine when to activate the fuel injectors.

For vehicles through 1992, a second reference signal is sent to the ECM which occurs at the same time as the sync-pulse, from the CKP sensor. This signal is called the 1X reference because it occurs 1 time per crankshaft revolution. The 1X and 2X reference signals are necessary for the ECM to determine when to activate the fuel injectors.

By comparing the time between the 1X and 2X, or 7X reference pulses, the ignition module/ICM 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 fir