Computer Controlled Coil Ignition (C3I)

In the EST mode, the ignition spark timing and ignition dwell time is fully controlled by the ECM. Above 450 rpm, the ECM applies 5.0 volts to the ignition module (bypass circuit) signaling the module to allow the ECM to control the dwell and spark timing. This is called EST mode. During EST mode, the ECM compensates for all driving conditions. The ECM relies on the following inputs to calculate the EST signal:

^ Crankshaft sensor
^ Coolant Temperature Sensor (CTS)
^ Mass Air Flow sensor (MAF)
^ Knock Sensor
^ Park/Neutral switch
^ Throttle Position Sensor (TPS)
^ Vehicle Speed Sensor (VSS)
To diagnose any of the above components refer to COMPUTERIZED ENGINE CONTROLS.

The EST system utilizes several input circuits. These input circuits include the Crank Reference, Bypass signal, the EST output, ESC (knock sensor), all of which are described below.

Crank Reference - This circuit provides the ECM with rpm and crankshaft position information from the ignition module. The ignition module receives the signal from the crank sensors hall effect switch. This signal will either be high or low, depending on the position of the interrupter ring. This high-low signal is used to trigger the ignition module for ignition operation and by the ECM to calculate fuel injection timing. Both the sync-pulse and crank sensor signals must be received by the ignition module in order for a reference signal to be produced on CKT 430. A loss of the reference signal would prevent the engine from running.

Bypass Circuit - The ECM either allows the ignition module to keep the spark advance at module mode 10° BTDC, or the ECM signals the ignition module that the ECM is going to control the spark advance EST mode. The ignition module determines the correct operating mode based on the level of voltage that the ECM sends to the ignition module on the bypass control circuit. The ECM provides 5.0 volts to the ignition module if the ECM is going to control spark timing EST mode. If the ECM does not turn ON the 5.0 volts, or if the ignition module doesn't receive it, the module will keep control of spark timing module mode. An open or grounded bypass control CKT 424 will set a code 42 and the ignition system will stay at module mode advance.

EST Circuit - The EST output circuitry of the ECM sends out timing pulses to the ignition module on this circuit. When in the module mode, the ignition module grounds these pulses. When in the EST mode, these pulses are the ignition timing pulses used by the ignition module to energize the ignition coils. Proper sequencing of the 3 ignition coils is always the job of the ignition module. If CKT 423 is open or grounded when the engine is started, a code 42 will set and the ignition system will stay in the module mode. If CKT 423 becomes open or grounded during EST mode operation, The engine will quit running but will restart. Upon restart, following an ignition cycle, a code 42 will be set, and the ignition will operate in module mode.

ESC Signal - The ESC system is comprised of a knock sensor and the ECM. The ECM monitors the ESC signal CKT 457 to determine when engine detonation occurs. When the knock sensor detects detonation, the ECM retards the timing EST to reduce detonation. Retarded timing can also be a result of excessive valve lifter, pushrod or other mechanical engine or transmission noise.

MODULE MODE

While the engine is being cranked the ignition module controls spark timing. This is known as bypass timing mode because the ignition module bypasses the ECM. The ignition system operates independently of the ECM, with module mode spark advance always at 10° BTDC. The ECM has no control of the ignition system when in this mode. In fact, the ECM could be disconnected from the car and the ignition system would still fire the spark plugs, as long as the other ignition system components were functioning. If an ECM/EST fault is detected while the engine is running, the ignition system will switch to the module mode. The engine may quit running, but will restart and stay in the module mode with a noticeable driveability complaint.