Idle air control valve

The coolant temperature sensor, is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the coolant temperature increases and the resultant signals sent to the ECM modify the injector opening time.

Intake air temperature sensor, is a temperature dependent resistor (thermistor). The resistance of the thermistor decreases as the air temperature increases and the resultant signals sent to the ECM modify the injector opening time.

Throttle position sensor, is a potentiometer which is connected to the primary throttle valve shaft. As the throttle angle changes, the throttle position sensor varies the voltage signal sent to the ECM to modify the injector opening time.

The ECM senses battery voltage and modifies the injector opening time to allow for variations in battery voltage. Low battery voltage can cause injector lag so reducing fuel delivery. The ECM compensates by increasing the injector opening time.

Idle air control valve

When the engine is cold, the automatic gearbox is in gear and the generator is under load, the ECM controls current to the idle air control (IAC) valve to maintain correct idle speed.

Fast idle thermo valve - up to 97.5 MY

To prevent erratic running when the engine is warming up, it is necessary to increase the idle speed. The fast idle thermo valve consists of a thermowax plunger which responds to changes in engine coolant temperature and therefore controls the amount of air allowed to by-pass the throttle valve.

NOTE: This valve was deleted at 97.5 MY.

Ignition timing and control

The system is controlled by the ECM and utilises several inputs also used to calculate fuel delivery.

The distributor incorporates the cylinder/crank position sensor, TDC sensor, ignition module, coil, rotor arm, and distributor cap to distribute the high tension (ht) output to the relevant spark plug.

From the following inputs the ECM determines the ignition timing. Cylinder/crank position sensor Manifold air pressure (MAP) sensor TDC position sensor Engine coolant temperature (ECT) sensor Throttle position (TP) sensor Intake air temperature (IAT) sensor Cranking signal Battery voltage

The data received from these inputs is used to provide an output to the following units: Ignition control module Distributor Spark plugs

ECM BACK-UP FUNCTIONS

Fail-safe function

When an abnormality occurs in a signal from a sensor, the ECM ignores that signal and assumes a pre-programmed value that allows the engine to continue to run.

Back-up function

When an abnormality occurs in the ECM itself, the injectors are controlled by a back-up circuit independent of the system in order to permit the car to be driven but with minimum performance.

Self-diagnosis function (Malfunction indicator lamp (MIL))

When an abnormality occurs in a signal from a sensor, the ECM supplies ground for the MIL and stores the failure code in erasable memory. When the ignition is initially turned on, the ECM illuminates the MIL for two seconds to check the condition of the bulb.