Deck 31: Mass Airflow Sensors

Question 1

A fuel-injection system that does not use a sensor to measure the amount (or mass) of air entering the engine is usually called a(n) _____________ type of system.

A) Air vane-controlled
B) Speed density
C) Mass airflow
D) Hot wire

Answer 1

The speed density type system of a fuel-injection system does not keep a sensor to determine the airflow volume into the engine. Before this system, a movable vane in the intake stream named vane airflow (VAF) sensor is used to measure the airflow volume into the system.
Hence, the correct option is
.

Question 2

How does a hot film MAF sensor work?

Answer 2

Working principle of the hot film MAF sensors :
A hot film mass airflow (MAF) sensor measures the temperature of the incoming air with the help of a temperature-sensing resistor. This temperature-sensing resistor is named as thermistor.
There is a conductive film in the sensor. The temperature of the conductive film is
higher than the temperature of the incoming air.
Since the amount and density of the air both causes cooling effect as the air passes through the sensor. This type of sensor produce an output depends upon the mass of the airflow because the product of the volume and the density of the air are equal to the mass of the airflow.
The amount of air entering the sensor is directly proportional to the amount of the hot film being cooled. As of result, the electronics inside the sensor scale up the current flow through the hot film in order to set the
temperature differential between the air temperature and the temperature of the hot film. This change in current flow is changed to a frequency output. This frequency output measures the amount of airflow. And finally the thermistor measures the temperature of the incoming air flow.

Question 3

Which type of sensor uses a burn-off circuit?

A) Hot wire MAF sensor
B) Hot film MAF sensor
C) Vane-type airflow sensor
D) Both a and b

Answer 3

When a wire is heated with an electric current that is rendered temporarily ineffective in the engine's air stream, the wire resistance goes up as the temperature of the wire goes up, which finally caps the current passing across the circuit. When air flows ended the wire, the wire cools down and the value of resistance goes down. As the result, more current flows through the circuit. It leads the temperature of the wire goes up until the resistance gets equilibrium again.
Hence, the correct option is
.

Question 4

What type of voltage signal is produced by a MAF?

Question 5

Which sensor has a switch that controls the electric fuel pump?

A) VAF
B) Hot wire MAF
C) Hot filter MAF
D) Karman Vortex sensor

Question 6

What change in the signal will occur if engine speed is increased?

Question 7

Two technicians are discussing Karman Vortex sensors. Technician A says that they contain a burn-off circuit to keep them clean. Technician B says that they contain a movable vane. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 8

How is a MAF sensor tested?

Question 9

The typical MAF reading on a scan tool with the engine at idle speed and normal operating temperature is _____________.

A) 1 to 3 grams per second
B) 3 to 7 grams per second
C) 8 to 12 grams per second
D) 14 to 24 grams per second

Question 10

What is the purpose of a MAF sensor?

Question 11

Two technicians are diagnosing a poorly running engine. There are no diagnostic trouble codes. When the MAF sensor is unplugged, the engine runs better. Technician A says that this means that the MAF is supplying incorrect airflow information to the PCM. Technician B says that this indicates that the PCM is defective. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 12

What are the types of airflow sensors?

Question 13

A MAF sensor on a General Motors 3800 V-6 is being tested for contamination. Technician A says that the sensor should show over 100 grams per second on a scan tool display when the accelerator is depressed to WOT on a running engine. Technician B says that the output frequency should exceed 7,000 Hz when the accelerator pedal is depressed to WOT on a running engine. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 14

Which airflow sensor has a dampening chamber?

A) A vane airflow
B) A hot film MAF
C) A hot wire MAF
D) A Karman Vortex

Question 15

Air that enters the engine without passing through the airflow sensor is called _____________.

A) Bypass air
B) Dirty air
C) False air
D) Measured air

Question 16

A P0102 DTC is being discussed. Technician A says that a sensor circuit shorted-to-ground can be the cause. Technician B says that an open sensor voltage supply circuit could be the cause. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B