In this chapter you have learned how the ECU electronically controls ignition timing, delivering spark at the optimum moment based on engine speed, load, temperature and quality of fuel. The spark advance curve is stored in a look up table in the ECU memory.
There are two types of ECU controlled spark advance systems used on Toyota TCCS equipped engines, the Variable Advance Spark Timing system (VAST) and the Electronic Spark Advance system (ESA). The main difference between these systems is the magnetic pickup in the distributor (Ne pickup) reports to the igniter on the VAST system and directly to the ECU on the ESA system.
An ignition confirmation signal is generated by the igniter which signals the ECU with each ignition event. The IGf signal is used to provide the ECU with a fail-safe fuel cutoff if ignition spark is lost.
The Distributorless Ignition system (DLI) provides secondary distribution by means of a three-coil waste spark system. Two companion spark plugs are connected to each end of the ignition coil secondary windings. These plugs fire simultaneously each time the cylinder pair approaches TDC, one spark igniting the mixture, the other wasted on the exhaust stroke.
Reprinted with permission from Toyota Motor Sale, U.S.A., Inc. from #850 EFI Course Book.
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