How can I check if the air flow sensor is OK?

The air flow sensor must determine the amount of air consumed by the engine. Based on the data received from the instrument, the engine control unit calculates the volume of fuel injected into the cylinders.

Possible "symptoms" of the malfunction of the flowmeter:

• The engine "does not hold" the revolutions at idle speed.
• Increased fuel consumption.
• The turbine is not connected in time or is not connected at all.
• Engine speed can be limited to 3,000 per minute.
• Possible speed limit. For example, a car can more or less actively pick up speed up to 100 km / h, after which the acceleration stops or becomes extremely slow.
• The machine significantly loses power.

Checking the mass air flow sensor is done with the help of special equipment - a compressor and an oscilloscope. Force the air flow to the sensor and monitor the signal range. It also determines the time for which the heating film is heated on the sensor.

When checking the output signal, the time taken by the transient at the time of ignition is first measured. In the case where the air flow sensor is OK, the value obtained will not exceed a few milliseconds. To increase the heating time of the sensor can cause pollution, which are deposited on the sensor element. In this case, the transient process can take tens and hundreds of milliseconds.

The value of the voltage is then measured with an air flow equal to zero. To check, it is necessary that the engine be stopped, but the ignition must be switched on. The normal value of the output voltage in the presence of zero air flow can be different and depends on whether the airflow sensor of which model is installed.

After this, the maximum value of the voltage is measured during a sharp overdrive. At the same time, the engine of the machine must be warmed to operating temperature and neutral transmission is switched on. During the test, the throttle valve opens sharply for a time not exceeding a second. This check is only possible for atmospheric engines (without a compressor and turbine), and if the accelerator pedal is mechanically connected to the throttle (via levers or rope).

When the engine is running without load at idle, the air in the intake manifold is extremely discharged. If the air flow sensor is functional, the signal voltage must exceed the 4V mark for a short time. If the sensor is heavily soiled, the sensor may react longer. In this case, the oscillogram is "smoothed out". Because of contamination, the heating current and the sensor signal decrease, which leads to a decrease in the fuel supply to the cylinders. Therefore, with a sharp overdrive, the voltage of the sensor signal does not reach the maximum values.

If serious faults in the operation of the instrument have been diagnosed, replace it. Repair of the mass air flow sensor is not performed.