Air box

The operating principle is based on a heated dia-phragm interposed in a measurement channel through which the intake air that goes to the engine flows.

The hot film diaphragm is kept at a constant tem-perature (about 120 °C above the temperature of the incoming air) by the heating resistance.

The mass of air that crosses the measurement channel tends to withdraw heat from the dia-phragm, therefore, to keep it at a constant tem-perature, a certain current must flow through the resistance.

This current is measured by a suitable Wheatstone bridge.

Therefore, the current is proportionate with the mass of flowing air.

The air flow meter directly measures the mass of air (not the volume) thereby eliminating problems of temperature, altitude, pressure, etc.

AIR BOX

REMOVAL/REFITTING

• Remove the pressure pump (see specific para-graph).

1. Disconnect the vacuum pipe from the E.G.R. valve.
2. Slacken the fastening screws and move aside the E.G.R. valve vacuum pipe.

• Disconnect the electrical connections from the glow plugs.

1. Slacken the injector side coupling of the pipes from the fuel manifold to the injectors using a suit-able wrench.
2. Slacken the manifold side coupling of the pipes from the fuel manifold to the injectors using tool no. 1.870.671.000.
3. Remove the fuel delivery pipes from the single fuel manifold to the injectors.

19 ÷ 23 Nm
1.9 ÷ 2.3 kgm

1. Disconnect the electrical connection from the fuel pressure sensor.
2. Slacken the fastening nuts and remove the fuel delivery manifold.