Ignition System: Description and Operation

Crankshaft Position Sensor 2.2L MFI:

Ignition Current Flow:

Ignition Control Wiring:

SYSTEM OPERATION
The Electronic Ignition (EI) system does not use the conventional distributor and coil. This ignition system consists of two separate ignition coils, Electronic Ignition Control Module (ICM) and Crankshaft Position (CKP) sensor as well as the related connecting wires and the Ignition Control (IC) portion of the Engine Control Module (ECM).

A distributorless ignition system uses a "waste spark" method of spark distribution. Each cylinder is paired with the cylinder that is opposite it (1 and 4 or 2 and 3). The spark occurs simultaneously in the cylinder coming up on the compression stroke and in the cylinder coming up on the exhaust stroke.

The cylinder on the exhaust stroke requires very little of the available voltage to fire the spark plug. The remaining energy will be used as required by the cylinder on the compression stroke. The same process is repeated when the cylinders reverses roles.

Under 400 RPM, the Ignition Control Module (ICM) controls spark timing (module timing mode) and over 400 RPM, the ECM controls spark timing (IC mode).

To properly control ignition timing, the ECM relies on the following information:
^ Engine load (manifold pressure)
^ Atmospheric pressure
^ Engine temperature
^ Manifold air temperature
^ Engine speed
^ Crankshaft position

To diagnose any of the above components refer to COMPUTERS AND CONTROL SYSTEMS.


IGNITION CONTROL
This system uses the same IC to ECM circuits that distributor type systems use. Following is a brief description for each of the IC circuits:

^ EI Reference (CKT 430) - The crankshaft position (CKP) sensor generates a signal to the ignition control module which results in a reference pulse being sent to the ECM. The ECM uses this signal to calculate crankshaft position and engine speed and injector pulse width.

^ Reference Ground (CKT 453) - This wire is grounded through the ignition control module and checks that the ground circuit has no voltage drop between the ignition module and the ECM, which could affect performance.

^ Bypass (CKT 424) - At about 400 RPM, the ECM applies 5 volts to this circuit to switch spark timing control from the ICM to the ECM.

^ IC (CKT 423) - The ICM sends a reference signal to the ECM when the engine is cranking. While the engine is under 400 RPM, the ICM controls the ignition timing. When the engine speed exceeds 400 RPM, the ECM applies 5 volts to the bypass line to switch the timing to ECM Ignition Control (IC).