What is a Vane Air Flow sensor (VAF)? How does the VAF Sensor work? What is the purpose of the VAF sensors? What are the symptoms of a VAF sensor malfunction?
Multi-point electronic fuel injection engines use air flow sensors. The computer that controls the amount fuel being sent to the combustion chamber (or ECU) is responsible for turning the fuel injectors off and on. The ECU is able to see the amount of air that has passed through the throttle plates via the air flow sensor. This information can be compared with other engine sensors to allow the ECU calculate the amount of fuel that the engine requires. To maintain the correct ratio of fuel and air, the ECU increases or decreases injector opening times.
Some engine types do not allow for airflow to be measured directly. The throttle position is calculated using data from sensors for manifold absolute and manifold temperature (MAP). Airflow can be measured directly on engines equipped with an EFI system using a mass airflow sensor or a vane (VAF), mass airflow sensor, and, for some Japanese vehicles, a “Karman-Vortex”, airflow sensor.
German Bosch L-Jetronic electronic fuel-injected vehicles, Japanese Nippondenso multiport electronic Fuel-Injection Vehicles produced under Bosch license and certain Ford vehicles with Bosch EFI system are used.
What is the Vane Air Flow Sensor?
The sensor is located in front of the throttle and uses a spring loaded mechanical vane to measure intake. Air entering the engine will cause the wing to open in proportion. The potentiometer receives the thrust force from the wing opening. Air intake can be calculated by changing the resistance of the sensor to determine the output voltage. The wing will open more if there is more air intake. This reduces the resistance of your potentiometer, and amplifies the voltage signal to the ECU.
Vane Air Flow Sensor includes a safety switch to protect the relay for electric fuel pump. The pump is driven by air flow. The engine will stop working if the fuel pump is not functioning. In such cases, it is important to check the air flow sensor.
A sealed idle mixture screw is also included in the sensor to regulate the amount of fuel mixture and control idle air.
Causes of failure in the Finned Air Flow Sensor
All other airflow sensors including the bladed airflow can’t tolerate air leaks. False information is sent to the ECU if there are any air leaks that can’t be measured by the sensor. Lean mixture can lead to engine misfires, sudden accelerations or idling fluctuations.
The sensor can also become clogged. Dirty air can cause the blade to stick or lose its mobility if it passes through an clogged filter. You can test the operation of your flap by gently pushing it with your finger. The flap should slowly open and close at the slightest resistance. You can use the electronic cleaner spray to get rid of any dirt that is stuck. The sensor will have to be replaced if it is not stuck.
The intake manifold kickbacks can cause the vane to move backwards quickly, which can lead to it being damaged or broken. A check valve is available for some sensors to protect it from kickback. Air leakage in the check-valve can lead to other problems over time. This will cause the sensor’s reading to be low and the engine may run in a rich mix.
Troubleshooting the Finned Air Flow Sensor
Bosch testers can also be used to verify the output voltage of legacy Bosch sensors. Multimeters are also available to verify the resistance and voltage of the terminals.
When the flap is in its closed position, and slowly opening, the output voltage from the sensor should be increased from 0.25 volts up to 4.5 V. The reference voltage (VRef), from the ECU, should be checked if the voltage value is too low. It should normally be 5 volts.
A Digital storage oscilloscope is the best tool to inspect for any leaks or dead spots in the sensor’s potentiometer. A functioning sensor should produce a steady and smooth voltage signal when the throttle opens fully at idle. The throttle can also be pressed slowly. Fuel injection timings should be adjusted if the voltage signal changes. As the VAF flap is opened, the open time for the injectors will increase.
The rheostat, or flow adjuster that senses the position of the air vane, often wears out. This is where most problems occur.
It is impossible to repair the Finned Airflow Sensor. If the unit malfunctions, it must be replaced completely. To clean the sensor housing or blade, you can use an electronic cleaner spray. You can save your fin from getting stuck in debris by using an electronic cleaner spray, but it won’t help with damaged covers or malfunctions.
