Title: Mass Air Flow Sensors
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2AIR FLOW SENSORS
- Port electronic fuel-injection systems that use
air flow volume for fuel calculation usually have
a movable vane in the intake stream. - The vane is part of the vane air flow (VAF)
sensor. - The vane is deflected by intake air flow.
FIGURE 17-1 A vane air flow (VAF) sensor.
3AIR FLOW SENSORS
FIGURE 17-2 A typical air vane sensor with the
cover removed. The movable arm contacts a carbon
resistance path as the vane opens. Many air vane
sensors also have contacts that close to supply
voltage to the electric fuel pump as the air vane
starts to open when the engine is being cranked
and air is being drawn into the engine.
4MASS AIR FLOW SENSOR TYPES
- Hot Film Sensor
- The hot film sensor uses a temperature-sensing
resistor (thermistor) to measure the temperature
of the incoming air. - Hot Wire Sensor
- The hot wire sensor is similar to the hot film
type, but uses a hot wire to sense the mass air
flow instead of the hot film.
5MASS AIR FLOW SENSOR TYPES
FIGURE 17-3 This five-wire mass air flow sensor
consists of a metal foil sensing unit, an intake
air temperature (IAT) sensor, and the electronic
module.
6MASS AIR FLOW SENSOR TYPES
FIGURE 17-4 The sensing wire in a typical hot
wire mass air flow sensor.
7KARMAN VORTEX SENSORS
FIGURE 17-5 A Karman Vortex air flow sensor uses
a triangle-shaped rod to create vortexes as the
air flows through the sensor. The electronics in
the sensor itself converts these vortexes to a
digital square wave signal.
8PCM USES FOR AIR FLOW SENSORS
- The PCM uses the information from the air flow
sensor for the following purposes - Air flow sensors are used mostly to determine the
amount of fuel needed and base pulse-width
numbers. - The greater the mass of the incoming air, the
longer the injectors are pulsed on. - Air flow sensors back up the TP sensor in the
event of a loss of signal or an inaccurate
throttle position sensor signal. - If the MAF sensor fails, then the PCM will
calculate the fuel delivery needs of the engine
based on throttle position and engine speed (RPM).
9TESTING MASS AIR FLOW SENSORS
- Start the testing of a MAF sensor by performing a
thorough visual inspection. - Look at all the hoses that direct and send air,
especially between the MAF sensor and the
throttle body. - Also check the electrical connector for
- Corrosion
- Terminals that are bent or pushed out of the
plastic connector - Frayed wiring
10TESTING MASS AIR FLOW SENSORS
- MAF Sensor Output Test
- Tap Test
- Digital Meter Test of a MAF Sensor
11HOT WIRE MAF SENSOR
TOYOTA COURSE 852 ENGINE CONTROL SYSTEMS
11
12MAF SENSOR CIRCUIT
TOYOTA COURSE 852 ENGINE CONTROL SYSTEMS
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13WHAT IS FALSE AIR?
FIGURE 17-6 Carefully check the hose between the
MAF sensor and the throttle plate for cracks or
splits that could create extra (false) air into
the engine that is not measured by the MAF sensor.
14Chapter 15
Mass Air Flow Sensors
MAF Sensor Grams per Second/Voltage Chart
Automotive Fuel and Emission Control Systems
15MAF SENSOR SIGNAL VOLTAGE
TOYOTA COURSE 852 ENGINE CONTROL SYSTEMS
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16Chapter 17
Mass Air Flow Sensors
- MAF Sensor Tap Test
- With the engine at idle speed, gently tap the
MAF sensor with the fingers of an open hand. If
the engine stumbles or stalls, the MAF sensor is
defective.
Automotive Fuel and Emission Control Systems
17Chapter 17
Mass Air Flow Sensors
- MAF Sensor Digital Meter Test
- Digital multimeter can be used to measure the
frequency (Hz) output of the sensor and compare
the reading with specifications.
Automotive Fuel and Emission Control Systems
18Chapter 17
Mass Air Flow Sensors
- CHAPTER SUMMARY
- A mass airflow sensor actually measures the
density and amount of air flowing into the
engine, which results in accurate engine control. - An air vane sensor measures the value of the air
and the intake air temperature sensor is used by
the PCM to calculate the mass of the air entering
the engine. - A hot-wire MAF sensor uses the electronics in the
sensor itself to heat a wire 70 C above the
temperature of the air entering the engine.
Automotive Fuel and Emission Control Systems