GM Corsica/Beretta 1988-1996 Repair Guide

General Information

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Vehicles which are equipped with the 2.0L, 2.2L, 2.8L and 3.1L engines utilize the Direct Ignition System (DIS). this system is called the Electronic Ignition (EI) system in later model years. This system features a distributorless ignition. The DIS/EI system consists of two separate ignition coils on 4-cylinder engines or 3 separate coils on V6 engines, and Ignition Control Module (ICM), and a secondary conductor housing which is mounted to an aluminum cover plate. The system also consists of on 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 guide, 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 consists of a knock sensor and 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 (ie. 1-4, 2-3 on 4-cylinder engines or 1-4, 2-5, 3-6 on 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 (TDC) at the same time. The one that is on compression is said to be the event cylinder and 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)
 

The ESC system is designed to retard spark timing up to 10 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.

SYSTEM COMPONENTS



Crankshaft Position (CKP) Sensor

See Figure 1

The Crankshaft Position (CKP) sensor is mounted remotely, next to the Ignition Control Module (ICM) on the 2.0L and 2.2L engines. The sensor is mounted remotely, on the opposite side of the engine from the module on the 2.8L and 3.1L engines located toward the bottom of the rear (right side) of the engine block on V6 engines. It is used to determine crankshaft position and engine speed.



Click image to see an enlarged view

Fig. Fig. 1: Crankshaft position sensor-to-crank reluctor relationship - 2.2L engine shown

Ignition Coils

See Figure 2

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



Click image to see an enlarged view

Fig. Fig. 2: The ignition coil assembly for the V6 engines has three separate coil assemblies. Note that 4-cylinder engines have only 2 separate coils

Electronic Spark Timing (EST)/Ignition Control (IC) System

The EST system, used on 1988-93 models, includes the following circuits:

These systems include 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/IC signal (CKT 423) - reference signal is sent to the ECM via the DIS module during cranking. Under 600 rpm, the IDI module controls the ignition timing. Above 600 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.
 

Ignition Control (IC)

The IC system, used on 1994-96 models, includes the following circuits:

2.2L ENGINE


Ignition control A & B (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 pules square wave 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.
 

3.1L ENGINE


3X Reference high (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.
 
3X 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 bypass (CKT 424) - During initial cranking, the PCM will look for synchronizing pulses from the camshaft and 3X crankshaft position sensor indicating the position of the no. 1 piston and intake valve. 5 volts are applied to the bypass circuit the instant these signals are received by the PCM. This generally occurs within 1 or 2 revolutions of the crankshaft. An open our grounded bypass circuit will set a diagnostic trouble code and the engine will run at base timing. A small amount of advance is built into the ignition control module to enhance performance.
 
Ignition control (CKT 423) - The PCM uses this circuit to trigger the electronic ignition control module. The PCM uses the crankshaft reference signal to base its calculation of the amount of spark advance needed under present engine conditions.
 
24X reference signal - Additional to the electronic ignition system is the 24X crankshaft position sensor. Its function is to smooth idle quality and provide improved low speed driveability.
 

 
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