Needle lift sensor (Engine management system - EDC)

Needle lift sensor

The needle lift sensor is located in the No. 1 injector body. It operates as the other injectors but has a coil which surrounds the shaft of an extended injection needle. The coil is fed a DC supply from the ECM which produces a magnetic field.

When the needle is moved under the influence of fuel pressure, the magnetic field is disturbed which induces an AC voltage in the coil. The induced voltage is registered in the ECM as a reference point for the start of the injection sequence.

The ECM uses the input signals from the needle lift sensor, together with a signal from the CKP sensor, to detect the actual start of injection. The ECM, using inputs from the other sensors, calculates then adjusts the injection timing of the fuel pump to achieve optimum fuelling of the engine.

If the needle lift sensor fails, the malfunction indicator lamp on the instrument panel is illuminated. The ECM, which enters a default mode, continues to function but with a reduction in engine performance and lack of throttle response.

Fuel Injection Timing Compensation

Engine Coolant Temperature (ECT) sensor

The ECT sensor is located in the top of the coolant outlet elbow which is attached to the front of the cylinder head. The sensor is screwed into a threaded port and measures the temperature of coolant as it leaves the engine via the top hose to the radiator.

The ECT sensor is a ’thermistor’ (a temperature dependent resistor), i.e. the voltage output varies in proportion to temperature. The ECM constantly monitors the signal and uses the information to correct the quantity of fuel injected and the injection timing especially during cold starting. During starting, output from the sensor determines the operating period for the glow plugs.

If the ECT sensor fails, the malfunction indicator lamp on the instrument panel is illuminated. The ECM uses a substitute value of -20°C for the injection timing and uses the fuel temperature to correct the fuel quantity.