763 Air Flow Meters

The air flow meter provides the ECM with a number of signals that are used in engine management. These signals include: measuring the air flow so that fuel injection matches it to give the correct air fuel ratio, indicating when the throttle valve is in the idle position, giving an indication of load on the engine etc. The commonly used types of air flow sensor have been described in Chapter 5 and the information given here is to show some practical tests that can be performed to assess the performance of air flow sensors.

The flap type (potentiometer) air flow sensor

In Fig. 7.17 the test probe is making contact with the signal connection on the air flow sensor. The time base of the oscilloscope must be set to a suitable value. If the throttle is moved steadily from fully closed to fully open and then released slowly, an oscilloscope trace similar to that shown in Fig. 7.18 should be obtained for the potentiometer type of sensor.

5 Specifications may vary. Consult manufacturer's specifications Fig. 7.17 Test connections for a MAF

4.9 6 V MAXIMUM 8 OLD mV MINIMUM

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