Basic ignition timing

BASIC IGNITION TIMING

Crankshaft position sensor

The speed and position of the engine is detected by the crankshaft position (CKP) sensor which is bolted to, and projects through, the engine adaptor plate adjacent to the flywheel.

The CKP sensor is an inductive sensor consisting of a bracket mounted body containing a coil and a permanent magnet which provides a magnetic field. The CKP sensor is situated so that an air gap exists between it and the flywheel. Air gap distance is critical for correct operation.

The flywheel incorporates a reluctor ring which consists of 32 poles spaced at 10° intervals, with 4 missing poles at 30°, 60°, 210° and 250°. The missing poles inform the ECM when to operate the groups of injectors. When the flywheel rotates, as a pole passes the CKP sensor it disturbs the magnetic field inducing a voltage pulse in the coil. This pulse is transmitted to the ECM.

By calculating the number of pulses that occur within a given time, the ECM can determine the engine speed. This is a primary input necessary to make the engine run.

Manifold absolute pressure sensor

The manifold absolute pressure (MAP) sensor is located within the ECM. It detects manifold pressure via a hose connected to the inlet manifold. The MAP sensor converts pressure variations into graduated electrical signals which can be read by the ECM. Increases and decreases in the manifold pressure provide the ECM with an accurate representation of the load being placed on the engine allowing the ECM to adjust the quantity of fuel being injected and the ignition timing to achieve optimum fuelling of the engine.