Economy gauge (Econometer)

Electrical system / Economy gauge (Econometer)

1 This device is fitted to ES (energy saving) models and indicates to the driver the fuel consumption (in litres per 100 km) coupled with a needle which moves over coloured sections of a dial to make the driver aware that his method of driving is either conducive to high or low fuel consumption. Refer to Chapter 3, Section 16.

2 The device is essentially a vacuum gauge which also incorporates a warning lamp to indicate to the driver when a change of gear is required.

3 A fuel cut-out valve (see Chapter 3, Section 11) is used in conjunction with the economy gauge so that when the accelerator pedal is released during a pre-determined engine speed range, fuel supply to the engine is stopped, but resumes when the engine speed falls below the specified range.

LED (light emitter diode) 4 The gearchange indicator will only light up at engine speeds in excess of 2000 rev/min for vacuum pressures up to 600 mm Hg in 1st, 2nd and 3rd speed gears and for vacuum pressures up to 676 mm Hg in 4th speed gear. The light will not come on if 5th speed gear is engaged or if the coolant temperature is below 55ºC.

5 There is a two second delay in the light coming on to prevent it operating during rapid acceleration in a low gear.

6 If the LED light comes on during deceleration it should be ignored.

Fault finding
7 A faulty economy gauge should be checked in the following way.

8 Refer to Section 21 and remove the instrument panel.

9 Disconnect the economy gauge L connector and then connect a test lamp between the BN cable contact and earth. If the lamp comes on then the gauge supply circuit is not open. If the lamp does not come on, check all connections in the supply cable which comes from the interconnecting unit of the electrical system, also Fuse No 12.

10 Now connect a voltmeter between the white cable and earth. Check the voltage with the engine not running, but the ignition switched on. It should be between 0.7 and 0.9 volt. If the reading varies considerably from that specified, check the connections between the economy gauge and the fuel cut-out device control unit. If the fault cannot be rectified, renew the ignition control unit (Digiplex system, see Chapter 4).

11 Now check the closed throttle valve plate switch by connecting a voltmeter between the brown and BN cables of the L connector. With the valve plate open, there should be no reading, but with it open, voltage should be indicated.

12 Failure to conform as described will be due to a faulty earth in the switch or a faulty fuel cut-out device control unit.

13 A further test of the throttle valve plate switch may be carried out by disconnecting the multi-plug from the fuel cut-out device control unit.

14 Connect a test lamp to contact 4 (positive battery terminal). The lamp should come on, when the engine is idling or the accelerator released. If it does not, renew the throttle valve plate switch.

15 Connect a tachometer to the brown/white cable contact in the L connector and record the engine speed with the engine running. If no reading is obtained, renew the Digiplex ignition control unit which must be faulty.

Fig. 9.14 Location of control units (Sec 33)

A Digiplex ignition system control unit B Fuel cut-out valve control unit