Toyota EFI/TCCS Ignition System Overview

The EFI/TCCS Ignition System. Overview of Toyota EFI/TCCS. Ignition Control. The ignition systems used on today’s. EFI/TCCS equipped engines are not that …

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Overview of Toyota EFI/TCCS Ignition Control
The ignition systems used on today\’s EFI/TCCS equipped engines are not that much different from the ignition system used on the original 4M-E EFI engine. Primary circuit current flow is controlled by an igniter based on signals generated by a magnetic pickup (pickup coil) located in the distributor. The ignition system has a dual purpose, to distribute a high voltage spark to the correct cylinder and to deliver it at the correct time. Ideal ignition timing will result in maximum combustion pressure at about 10\’ ATDC.
The most significant difference between TCCS and Conventional EFI ignition systems is the way spark advance angle is managed. The Conventional EFI system uses mechanical advance weights and vacuum diaphragms to accomplish this. Starting with the 5M-GE engine in 1983, the TCCS system controls ignition spark timing electronically and adds an ignition confirmation signal as a fail-safe measure. There are two versions of electronic spark management used on TCCS equipped engines, the Electronic Spark Advance (ESA) and the Variable Advance Spark Timing (VAST) systems.
Conventional EFI Ignition System
Spark Advance Angle Control In the Conventional EFI system, spark advance angle is determined by the position of the distributor (initial timing), position of the magnetic pickup reluctor teeth (centrifugal advance), and position of the breaker plate and pickup coil winding (vacuum advance). The spark advance curve is determined by the calibration of the centrifugal and vacuum advance springs. Besides being subject to mechanical wear and mis-calibration, this type of spark advance calibration is very limited and inflexible when variations in coolant temperature and engine detonation characteristics are considered. Mechanical control of a spark curve is, at best, a compromise. In some cases the timing is optimal; in most cases it is not. Engine RPM Signal To indicate engine rpm to the EFI computer, the Conventional EFI system uses the signal generated at the coil negative terminal (IG-). Because this system does not use ECU controlled timing, the rpm signal to the ECU has no impact on spark timing whatsoever. The IG signal is used as an input for fuel injection only.

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