AIR MONITORING DEVICES Submitted by :- GURDIT SINGH
INTRODUCTION OF AIR MONITORING DEVICES
Bosch introduced its first MAP sensor in 1967 called the D-Jetronic ,D standing for German word Druck meaning pressure.
MAP sensor technology changed dramatically in mid 80’s with introduction of piezo- crystal type sensor
MASS AIR FLOW SENSORS
The Mass Air Flow Sensors are used to calculate the amount of air entering the engine.
What is the use of MAF in cars ?
The information collected by the air flow sensors regarding the mass of air entering the engine is used by the ECU to determine:-
how much fuel to inject
When to ignite the cylinders
Shifts the transmission.
LOCATION OF AIR FLOW SENSORS Air cleaner AIR FLOW SENSOR Throttle body Air Intake Chamber Intake Manifold Cylinders The air flow sensor is located between the air cleaner and throttle body.
TYPES OF MAF SENSORS
There are 2 types of MAF sensors:-
1) Vane Airflow Sensor
2) Hot Wire Air Flow Sensor
VANE AIR FLOW SENSOR The vane air flow sensor consists of the following parts:- 1) Potentiometer 2) Air temperature sensor 3) Idle mixture screw 4) Fuel pump switch 5) By pass air passage 6) Spring loaded mechanical flap
WORKING OF VANE AIR FLOW SENSOR
The VAF sensor monitors the volume of air entering the engine through spring loaded mechanical flap.
The flap is pushed open by amount that is proportional to the volume of air entering the engine
Movement of flap Volume of air entering the engine
Where x and y are movement and volume respectively
So the greater the airflow, further the flap opens
The flap has a arm allowing the sensors resistance and output voltage to change according to air flow.
The greater the air flow, further the flap opens and this lowers the potentiometer resistance and increase the voltage return signal to the computer.
TESTING VAF SENSORS
Use a Multimeter to check the voltage and resistance values across various terminals.
The sensor's output voltage should rise from around 0.25 volts up to about 4.5 volts as the flap goes from closed to open.
Watching a vane airflow sensor's output on a digital storage oscilloscope (DSO) is a good way to detect " skips " or dead spots in the sensor's internal potentiometer
PROBLEMS OCCURING IN VANE AIRFLOW SENSOR
Vane airflow sensors can't tolerate air leaks.
Air leaks can allow " unmetered " or " false " air to enter the engine.
The extra air can lean out the fuel mixture causing problems like:-
Stumbling when accelerating
2) Dirt can also cause problems.
Unfiltered air passing can allow dirt to build up on the flap causing the flap to bind or stick.
3) Backfiring in the intake manifold can force the flap backwards violently, often bending or breaking the flap.
SOLUTION FOR PROBLEMS
1)Problems related to flap movement could be diagnosed using a finger to check if flap opens and close with even resistance.
If it binds or sticks a shot of carburetor cleaner may loosen it up
2)Check for air leaks
3)Vane air flow sensors should be replace if there is an internal fault
HOT WIRE MAF SENSOR The hot wire MAF sensor consists of following parts:- 1)Thermistor 2)Platinum hot wire 3)ECU
WORKING OF HOT WIRE MAF SENSOR
The phenomenon is to heat the wire with an electrical current that is suspended in engine’s air stream.
The electrical resistance increases as the wire temperature increases which helps to regulate the current flowing through the circuit
When the air flows past the wire:-
the temperature decreases hence resistance decreases hence more current flows
As more current flow the resistance increases again until it reaches the equilibrium again.
current required to maintain the wire’s temperature mass of air flowing past the wire
The integrated electronic circuit converts the measurement of current into a voltage signal which is sent to the ECU
BENEFITS OF HOT WIRE MAF SENSOR
1) Responds quickly to changes in air flow
2) Less expensive
3) More durable due to non moving parts
PROBLEMS SEEN IN HOT WIRE MAF SENSOR
The main problem occurring in the Hot wire MAF is :-
Contamination of the sensing wire element known as “ growing hairs”
Causes of growing hair :-
dirt from cheap air filters sticking to the sensing wire element.
Problems caused by growing hair
This shields it from the incoming air.
This causes air-fuel ratio control problems.
MAP SENSOR A manifold absolute pressure sensor (MAP) provides manifold pressure to the ECU.
WORKING OF MAP SENSORS The MAP sensor consists of:- 1)Silicon chip 2)Vacumn chamber 3)Filter
WORKING OF MAP SENSOR
In the MAP sensor there is a silicon chip mounted inside the reference chamber
On one side of chip is reference pressure
On other side is the pressure to be measured
The silicon chip changes its resistance with changes in pressure
This change in resistance alters the voltage signal
The ECM interprets the voltage signal to measure engine load
Hence the ECM is able to figure out:-
how much fuel to inject
when to ignite cylinders
TYPES OF MAP SENSORS
There are two types of MAP sensors .
1)The typical MAP sensor senses pressure (vacuum) in the manifold.
2)The other helps the PCM estimate air flow in addition to pressure changes in the manifold.
This type of MAP sensor is found on vehicles with speed density fuel injection
PROBLEMS DUE TO FAULTY MAP SENSOR
1) It could cause the car to not start, but that is rarely seen
2) It causes hesitation on acceleration
3) Poor engine performance
4) Poor gas mileage
5) Black smoke coming from the exhaust (high emissions).
DIAGNOSING MAP SENSORS
Use a scan tool to ensure there is a problem with map sensor
Check the Vacumn hose
Check the electrical connections
Check circuit wires for damage
Replace Map sensor if ground is present .
Altogether we can say that Air monitoring devices play an essential part in engine management systems by measuring the volume, density and pressure of air entering the engine at any given time. Hence providing the computer with essential information which in turn results in better performance and increase the efficiency of the engine.