GM Cavalier/Sunfire 1995-2000 Repair Guide

General Information

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The Distributorless Ignition System or Electronic Ignition (EI) system does not use the conventional distributor and ignition coil. The system consists of 2 separate ignition coils, an Ignition Control Module (ICM), crankshaft sensor, Camshaft Position (CMP) sensor, along with the related connecting wires and the Ignition Control (IC) portion of the powertrain control module (PCM).

The distributorless system uses a waste spark method of spark distribution. Companion cylinders are paired and the spark occurs simultaneously in the cylinder with the piston coming up on the compression stroke and in the companion cylinder with the piston coming up on the exhaust stroke.

The cylinder on the exhaust stroke requires very little of the available voltage to arc, so the remaining high voltage is used by the cylinder in the firing position (TDC compression). This same process is repeated when the companion cylinders reverse roles.

It is possible in an engine no-load condition, for one plug to fire, even though the spark plug lead from the same coil is disconnected from the other spark plug. The disconnected spark plug lead acts as one plate of a capacitor, with the engine being the other plate. These two capacitor plates are charged as a current surge (spark) jumpe across the gap of the connected spark plug.

These plates are then discharged as the secondary energy is dissipated in an oscillating current across the gap of the spark plug still connected. Because of the direction of current flow in the primary windings and thue in the secondary windings, one spark plug will fire from the center electrode to the side electrode, while the other will fire from the side electrode to the center electrode.

These systems utilize the IC signal from the PCM, as do some convention distributor type ignition systems.

In the Direct Ignition or Electronic Ignition system while under 400 rpm, the ICM controls the spark timing through a module timing mode. Over 400 rpm, the PCM controls the spark timing through the IC mode. To properly control the ignition timing, the PCM relies on information from the various sensors including the following:



Manifold Absolute Pressure (MAP) sensor
 
Engine Coolant Temperature (ECT) sensor
 
Intake Air Temperature (IAT) sensor
 
Crankshaft position
 
Knock sensor (KS)
 
Throttle Position (TP) sensor
 

SYSTEM COMPONENTS



Crankshaft Position (CKP) Sensor

See Figure 1

A magnetic crankshaft sensor (Hall Effect switch) is used to provide the ICM and PCM with engine speed data. The sensor protrudes in to the engine block, within about 0.050 in. (1.27mm) of the crankshaft reluctor.



Click image to see an enlarged view

Fig. Fig. 1: View of the CKP sensor-to-crankshaft reluctor relationship

The sensor is a fixed mount magnetic sensor that has voltage induced by a rotating reluctor wheel. The reluctor is a special wheel cast into the crankshaft with seven slots machined into it, six of which are equally spaced 60° apart. A seventh slot is spaced 10° from one of the other slots and serves as a generator of a sync-pulse. as the reluctor rotates as part of the crankshaft, the slote change the magnetic field of the sensor, creating an induced voltage pulse.

The CKP sensor sends a signal to the ICM which sends a reference signals to the PCM, based on the Crankshaft Position (CKP) sensor pulses, which are used to determine crankshaft position and engine speed. Reference pulses to the PCM occur at a rate of 7 per 360° of crankshaft rotation. this signal is called the 7X reference because it occurs 7 times per crankshaft revolution.

The 7X reference signal is necessary for the PCM to determine when to activate the fuel injectors.

The PCM activates the fuel injectors, based on the recognition of every other reference pulse, beginning at a crankshaft position 120° after piston Top Dead Center (TDC). By comparing the time between the pulses, the Ignition Control Module (ICM) can recognize the pulse representing the seventh slot (sync-pulse) which starte the calculation of ignition coil sequencing.

Ignition Coils

There are two separate coils for the 2.2L and 2.3L/2.4L engines mounted to the coil/module assembly. Spark distribution is synchronized by a signal from the crankshaft sensor which the ignition module uses to trigger each coil at the proper time. Each coil provides the spark for two spark pluge simultaneously (waste spark distribution).

The coils are mounted to the ICM. Each coil can be replaced separately. A fused low current source to the module terminal M , providee power for the sensors, ignition coils and internal module circuitry.

Ignition Control Module (ICM)

The DIS module or ICM, as it's called in later years, monitors the crankshaft sensor signal, then, based on these signals, sends a reference signal to the powertrain control module (PCM) so that correct spark and fuel injector control can be maintained during all driving conditions. During cranking, the module monitors the sync-pulse to begin the ignition firing sequence. Below 400 rpm, the module controls the spark advance by triggering each of the ignition coils at a predetermined interval, based on engine speed only. Above 100 rpm, the PCM controls the electronic spark timing (EST) and compensates for all driving conditions. The module must receive a sync-pulse and then a crank signal, in that order, to enable the engine to start.

The DIS module or Ignition Control Module (ICM) is not repairable. When a module is replaced, the remaining DIS/ICM components must be transferred to the new module.

Ignition Control (IC)

The IC system is a series of circuits between the ICM and the PCM that are used to send information about the ignition system. This system includes the following circuits:



7X Reference -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-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 -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.
 

 
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