Manifold absolute pressure sensor

Manifold absolute pressure sensor

The manifold absolute pressure (MAP) sensor is fixed directly to the inlet manifold. The ECM provides a 5 volt supply and earth path to the sensor. The sensor then returns a voltage output which represents the pressure. 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 calculate both the ignition timing and quantity of fuel to be injected to achieve optimum fuelling of the engine. The voltage supply for this sensor is provided directly from the ECM.

IGNITION TIMING COMPENSATION - VVC

Engine coolant temperature sensor

The engine coolant temperature sensor is a ’thermistor’ (a temperature dependent resistor), i.e. the voltage output varies in proportion to temperature. The sensor is located in the front of the coolant outlet elbow. The ECM constantly monitors this signal and uses the information to provide optimum driveability and emissions by advancing or retarding the ignition timing.

Idle speed control

With the throttle pedal released and the engine at idle, the ECM uses the fast response of the engine ignition timing to maintain idle stabilisation.

When loads are placed on or removed from the engine, the ECM senses the change in engine speed and in conjunction with adjusting the idle air control valve, advances or retards the ignition timing to maintain a specified idle speed. When load is removed from the engine, the idle air control valve returns to its original position and the ignition timing returns to the idle setting.

NOTE: Due to the sensitivity of this system, the ignition timing will be constantly changing at idle speed.