Ignition System: Description and Operation

DESCRIPTION

ELECTRONIC SPARK ADVANCE (ESA)

The Engine Control Module (ECM) is programmed with data for optimum ignition timing under all operating conditions. Using data provided by sensors which monitor various engine functions (rpm. intake air volume, engine coolant temperature, etc.), the ECM triggers the spark at precisely the right instant.

OPERATION

Timing signals are generated through magnetic induction by the pick-up coils, as in conventional electronic ignition systems. These signals are transmitted directly to the Toyota Computer Controlled System (TCCS) ECM rather than to the igniter assembly. The TCCS ECM is programmed with optimum ignition timing values for all operating conditions. It uses signals from the pick-up coils to compute crankshaft position and signals from other sensors to compute engine and vehicle operating conditions, then adjusts ignition timing by controlling the switching function of the igniter assembly. The igniter assembly controls current flow through the ignition coil primary circuit, and therefore induction of secondary spark voltage.

CONSTRUCTION

The ignition system includes an induction type ignition coil, igniter assembly, a single, twin or triple pick-up distributor, and electronic spark advance Electronic Spark Advance (ESA) circuitry located in the TCCS ECM. A specially constructed distributor cap, rotor and spark plugs are used to insulate higher secondary voltages produced by the ignition coil. There are no centrifugal or vacuum advance mechanisms, as spark timing is controlled entirely by the ESA.