Fuel system - MPi (page 2 of 7)

Intake air temperature sensor

The intake air temperature (IAT) sensor is located in the side of the inlet manifold. The IAT sensor is of the negative temperature coefficient (NTC) type, designed to reduce its resistance with increasing temperature.

The ECM receives a signal from the IAT sensor proportional to the temperature of the intake air. When this signal is used in conjunction with the signal from the manifold absolute pressure sensor. The ECM calculates the volume of oxygen in the air and adjusts the quantity of fuel being injected, to achieve optimum fuelling of the engine.

Injectors

The four fuel injectors are fitted between the pressurised fuel rail and inlet manifold. Each injector comprises a solenoid operated needle valve and a specially designed nozzle to ensure good fuel atomisation.

The injectors are controlled in grouped mode with 2 & 3 being grouped and 1 & 4 being grouped, with the injectors in each group being operated alternatively. The ECM determines when to operate the injectors based on the signal it receives from the crankshaft position sensor.

The ECM provides an earth signal for the period the injectors are required to be open, the injector solenoids are energised and fuel is sprayed into the inlet manifold onto the back of the inlet valves. The ECM carefully meters the amount of fuel injected by adjusting the injector opening period (pulse width). During cranking, when the engine speed is below approximately 400 rev/min, the ECM increases the injector pulse width to aid starting. The amount of increase depends upon engine coolant temperature. To prevent flooding, the ECM periodically inhibits the operation of the injectors.

Throttle housing

The throttle housing is located between the inlet manifold and air intake hose and is sealed to the manifold by an ’O’ ring. The throttle housing incorporates a throttle disc which is connected to the throttle pedal via the throttle lever and a cable.

There are two breather pipes connected to the throttle housing, one either side of the throttle disc. When the engine is running with the throttle disc open, both pipes are subject to manifold depression and draw crankcase fumes into the manifold. When the throttle disc is closed, only the pipe on the inlet manifold side of the disc is subject to manifold depression. This pipe incorporates a restrictor to prevent engine oil being drawn into the engine by the substantially greater manifold depression.

Mounted on the throttle housing are the throttle position sensor and idle air control valve.