Mass Air Flow (MAF) Sensors

Mass Air Flow (MAF) Sensors. The Mass Air Flow Sensors converts the amount of air drawn into the engine into a voltage signal. The ECM needs to know intake …

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Mass Air Flow (MAF) Sensors
Diagnosis of the MAF sensor involves visual, circuit, and component checks. The MAF sensor passage must be free of debris to operate properly. If the passage is plugged, the engine will usually start, but run poorly or stall and may not set a DTC.
Vane Air Flow Meter The Vane Air Flow Meter provides the ECM with an accurate measure of the load placed on the engine. The ECM uses it to calculate basic injection duration and basic ignition advance angle. Vane Air Flow Meters consist of the following components: * Measuring Plate. * Compensation Plate. * Return Spring. * Potentiometer. * Bypass Air Passage. * Idle Adjusting Screw (factory adjusted). * Fuel Pump Switch. * Intake Air Temperature (IAT) Sensor.
During engine operation, intake air flow reacts against the measuring plate (and return spring) and deflects the plate in proportion to the volume of air flow passing the plate. A compensation plate (which is attached to the measuring plate) is located inside a damping chamber and acts as a \”shock absorber\” to prevent rapid movement or vibration of the measuring plate. Movement of the measuring plate is transferred through a shaft to a slider (movable arm) on the potentiometer. Movement of the slider against the potentiometer resistor causes a variable voltage signal back to the VS terminal at the ECM. Because of the relationship of the measuring plate and potentiometer, changes in the VS signal will be proportional to the air intake volume.
The r2 resistor (connected in parallel with r1) allows the meter to continue to provide a VS signal in the event that an open occurs in the main potentiometer (r1). The Vane Air Flow Meter also has a fuel pump switch built into the meter that closes to maintain fuel pump operation once the engine has started and air flow has begun. The meter also contains a factory adjusted idle adjusting screw that is covered by a tamper resistant plug. The repair manual does not provide procedures on resetting this screw in cases where it has been tampered with. Types of VAF Meters There were two major types of VAF meters. The first design, is the oldest type. It uses battery voltage for supply voltage. With this type of VAF meter, as the measuring plate opens signal voltage increases.
Karmen Vortex Air Flow Meter This air flow meter provides the same type of information (intake air volume) as the Vane Air Flow Meter. It consists of the following components: * Vortex Generator. * Mirror (metal foil). * Photo Coupler (LED and photo transistor). Karman Vortex Air Flow Meter Operation Intake air flow reacting against the vortex generator creates a swirling effect to the air downstream, very similar to the wake created in the water after a boat passes. This wake or flutter is referred to as a \”Karman Vortex.\” The frequencies of the vortices vary in proportion to the intake air velocity (engine load).
The vortices are metered into a pressure directing hole from which they act upon the metal foil mirror. The air flow against the mirror causes it to oscillate in proportion to the vortex frequency. This causes the illumination from the photo coupler\’s LED to be alternately applied to and diverted away from a photo transistor. As a result, the photo transistor alternately grounds or opens the 5-volt KS signal to the ECM.
This creates a 5 volt square wave signal that increases frequency in proportion to the increase in intake air flow. Because of the rapid, high frequency nature of this signal, accurate signal inspection at various engine operating ranges requires using a high quality digital multimeter (with frequency capabilities) or oscilloscope.

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