Purpose of Spark Advance Control Systems

The amount of spark advance needed by the engine varies depending on a number of different operating conditions. Generally, spark advance follows the following strategy:

• spark advance increases with higher engine speeds for performance and fuel economy.

• spark advance needs to decrease under heavy load conditions to avoid detonation.

They are many variables the system must consider when determining the proper spark lead time. Coolant temperature, fuel quality, and engine load are just a few of the many factors that can significantly impact ideal ignition time. The ECM determines proper spark timing by applying various input signals against a preprogrammed spark advance strategy or "map".

Fuel injected Toyota vehicles use either a mechanical or electronic spark advance control system. They are referred to as either conventional EFI ignition system (mechanical), Variable Advance Spark Timing (VAST) or Electronic Spark Advance (ESA).

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