They still do suffer from the drawback of having a dwell time that varies with engine speed. A case of too much energy at a low speed and not enough energy at high rpm requires the next level of ignition system controls. Although breakerless systems show considerable improvement over the breaker-triggered types, they still have a disadvantage with regard to the spark timing. These systems typically use centrifugal and vacuum advance units on the distributor and are considered to be a poor match for today s electronics and engine efficiency. A computer program is used to calculate the best ignition timing for the current engine operating condition.
Initial timing is never less than the initial advance.
Basic advance is the advance value obtained from the timing map in line with the engine load and speed conditions. Correction advance is the advance that may be added for current engine operating conditions, such as warm-up, overheating, idle and knock control. The results of these ignition calculations are a switching signal that controls the timing of the ignition coil primary current. Every system has a power feed and ground circuit for the ignition primary. This can serve as a common diagnosis point on all ignition systems, including both the DI and EI control circuit and is usually easy to access.