The purpose of this test is to evaluate the voltage output and response time of the Air Flow Meter during engine idle, WOT and over-run conditions.
Carry out a WOT throttle test to capture your data.
The example waveform shows an engine idle voltage of around 1.75 V. On the time scale between 1.25 s and 1.5 s you can see the initial rapid rise and slight levelling of the voltage. This is due to the initial influx of air as the throttle opens. The air flow then increases to maximum and the meter output records just under 4 V.
As the throttle closes the voltage falls. At a point around 3.5 s you can see a short levelling and then a more gradual decrease in voltage. This is an anti-stall feature and usually activates at around 1200 RPM.
The hash or oscillations in the waveform are caused by the induction pulses as the engine runs.
The Bosch common rail diesel system may be either turbocharged or normally aspirated. In both cases the airflow sensor is located next to the air filter.
The airflow meter monitors the volume of air and supplies the ECM with the relevant data. It uses a conventional method of monitoring the flow by means of controlling the temperature of a heated platinum wire. The incoming air passes over the hot wire cooling it and altering the output voltage. The voltage at the AFM output terminal is directly proportional to air flow, increasing as the airflow increases.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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