Actual Teeth vs Internal Teeth

Overview

There is a difference between actual teeth on the crankshaft wheel and internal teeth used by the ECU for triggering ignition or injection events.

Internal teeth always coincide with actual teeth but they are arranged such that they are at evenly spaced crank angles.

Actual Teeth vs Internal Teeth

Events from ‘actual teeth’ on the crankshaft wheel cause the ECU’s CPU to be interrupted. The ECU decides whether these events are ‘active edges’ aka ‘internal teeth’ that may be used for triggering ignition or injection events.

If using a missing / extra tooth strategy, the actual tooth events are not evenly spaced. The ECU is able to detect this un-even spacing to identify missing / extra teeth.

If the engine cycle can be determined from a camshaft sensor, and sequential injection or ignition is required, then the Fuel Teeth and Spark Teeth options should wither be set to the same value as the number of internal teeth (e.g. wasted spark) or to double the value (sequential).