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 fire No. 2-3 ignition coil and the fifth crank pulse signals the module to fire the No. 1-4 ignition coil.



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Fig. Fig. 1: Relationship of the Crankshaft Position (CKP) sensor to the crankshaft reluctor

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 computer control module controls the spark timing (EST or IC) 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 spark timing the ECM/PCM uses the following inputs:



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

The ESC system is designed to retard spark timing up to 15° to reduce spark knock in the engine. When the knock sensor detects spark knocking in the engine, it sends an AC voltage signal to the computer control module, which increases with the severity of the knock. The ECM or PCM then adjusts the EST/IC to reduce spark knock.

SYSTEM COMPONENTS



Crankshaft Position (CKP) Sensor

The Crankshaft Position (CKP) sensor (formerly named simply crankshaft sensor), mounted remotely from the ignition module on an aluminum cover plate, is used to determine crankshaft position and engine speed.

Ignition Coils

The two ignition coil assemblies are mounted inside the module assembly housing. Each coil distributes the spark for two plugs simultaneously (waste spark distribution).

Electronic Spark Timing (EST)
1988-92 VEHICLES

The EST system is basically the same EST to ECM circuit used on the distributor type ignition systems with EST. This system includes the following circuits:



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 45)-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.
 

Ignition Control (IC)
1993-98 VEHICLES

The IC system uses circuits between the Ignition Control Module (ICM) and the PCM similar to the type that distributor systems use. This system includes the following circuits:



7X Reference (CKT 430)-The CKP sensor generates a signal to the ICM, resulting in a reference pulse which is sent to the PCM. The PCM uses this signal to determine crankshaft position, engine speed and injector pulse width. The engine will not start or run if this circuit is open or grounded.
 
Reference low (CKT 453)-This wire is grounded through the module and insures that the ground circuit has no voltage drop between the ICM and the PCM which may affect engine performance.
 
Ignition control 1 & 2 (CKTs 423 & 406)-The PCM sends the Ignition Control (IC) pulses to the ICM on these circuits. These signals are similar to the 7X reference pulse except that the PCM uses sensor inputs to determine the pulse timing to control spark advance. When the PCM receives the 7X signal, it will determine which pair of cylinders will be fired. (1-4 or 2-3). It will tell the ICM which cylinder pair will be fired via CKTs 423 or 406.
 

Electronic Spark Control (ESC) Sensor/Knock Sensor (KS)

The ESC or Knock sensor, mounted in the engine block near the cylinders, detects abnormal vibration (spark knock) in the engine. It produces an AC output voltage which increases with the severity of the knock. This signal goes to the computer control module (ECM/PCM) then adjusts the EST or IC to reduce spark knocking.

 
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