Federal Emissions

Ignition System Circuit Diagram:

PURPOSE:
In much the same manner as the distributor type ignition system, this system uses the Ignition Control (IC) signal from the ECM. The ECM controls the spark above 400 RPM and compensates for all driving conditions. The ECM relies on the following inputs to calculate the IC signal:
^ Calculated BARO
^ Engine Coolant Temperature (ECT) Sensor
^ Crankshaft sensor
^ Engine speed
^ Knock Sensor
^ MAP sensor
^ Intake Air Temperature (IAT) sensor

To diagnose any of the above components refer to COMPUTERIZED ENGINE CONTROLS.

CONSTRUCTION:
The Electronic Ignition (EI) is a distributorless type ignition system which consists of a crankshaft sensor (CKP), the Ignition Control (IC) portion of the Electronic Control Module (ECM), three separate ignition coils, and an ignition module.

OPERATION:
The crankshaft sensor sends a signal through the ignition module to the ECM. The ECM uses this reference signal to calculate engine speed and crankshaft position. The Knock Sensor (KS) system is part of the ECM and is used as an input for the IC control of the EI module.

Ignition Current Flow:

Three separate coils are mounted to the module assembly. Each coil provides the spark for two plugs simultaneously. Each coil can also be replaced separately. A "Waste Spark" method of distribution is used on this system. Each cylinder is paired with its opposing cylinder in firing order so that one cylinder on the compression stroke fires simultaneously with its opposing cylinder on the exhaust stroke. Requiring less voltage to fire the plug on the exhaust stroke, most of the available voltage is sent to the compression stroke cylinder. This process is reversed as the cylinders' roles are reversed.

The ignition module controls spark timing under 400 RPM and must receive a "sync-pulse" followed by a Crank Signal in that order to enable engine start up. The ignition module monitors the crankshaft sensor signals and based on these signals, sends a reference signal to the ECM to allow the correct spark and fuel injector control to be maintained during all driving conditions.

CIRCUIT AFFECTING IGNITION CONTROL
The IC system consists of the EI assembly (coils, module, and crankshaft sensor), ECM and connecting wires. The EI control module are shown above. These circuits perform the following functions:

EI Reference (CKT 430) - The crankshaft position sensor sends a signal to the electronic ignition control module which generates a reference pulse which is sent to the ECM. The ECM uses this signal to calculate crankshaft position and engine speed (also used to trigger the injector).

Reference Ground (CKT 453) - This wire is grounded through the module and makes sure the ground circuit has no voltage drop between the ignition module and the ECM, which if open, could affect performance.

Bypass (CKT 424) - At about 400 rpm the ECM applies 5 volts to this circuit to switch timing from the electronic ignition control module to the ECM. An open or grounded bypass circuit will set a DTC 42 and the engine will run a base timing. A small amount of advance is built into the ignition control module to enhance performance.

Ignition Control (IC) (CKT 423) - The ECM uses this circuit (when bypass voltage is applied) to trigger the EI control module. The ECM uses the crankshaft reference signal to base its calculation of the amount of spark advance needed under present engine conditions.