This is the component normally mounted between the throttle body and the end of the intake manifold passages. It's purpose is to have a configuration where we can set a sensor up that will react with what's happening through the whole air intake tube to feed the ECU with important information about how to run the engine.
No argument, ECU is a computer, so the signal that this particular type of MASS AIRFLOW SENSOR or ANY type of M.A.F give has to be in Voltage signal. It's called VANE or FLAP MAS because the basic concept is: aerodynamic/mechanical reactions of the flap/vane according to how big the flow of air is, will be turned into voltage signal feeding to the ECU by a mechanical link between flap movement and a variable resistor in series with the line where Vsignal is coming out. So if we have a variable resistor, in a configuration where voltage divider applies, it will control the outcome voltage, not necessarily Ohm's Law this time!
There is a small circuit inside this little device, well every sensor needs their cute little circuitry obviously. In this particular Vane MAFS, you will see there are 7 electrical pins coming out of the plug of where the square little black plastic box sealed on the flap body. Those 7 pins represent the relationship of this circuit with "the rest of the car's circuit". Well of course in this case "the rest" is referred to ECU because this sensor seems to be simple enough that it only needs to answer to the ECU.
So this circuit is not complete, but it will run by itself like any other circuit if we just supply a little bit of voltage through the right pin. And NOT every part of any of these circuitry that appears inside the little box.
There are 3 main parts represented by those 7 pins: The thermistor circuit; The Main vane voltage output signal circuit, and the Fuel pump switch circuit. Yet they seem physically connected but their operations in terms of circuitry are separate.
The thermistor circuit, convenient to locate close to the signal output circuit, because when we built a sensor to measure how big the volume of air flowing through per second, we thing why not include air temperature measurement too: Temperature-Volume-Pressure are inseparable when talking about air/gas.
So in the wiring diagram, we can see that this circuit only needs an Earth for itself (E2), and everything comes out is temperature, because there is another sub-materialized circuitry inside the little nob that sticks out inside the air passage as well. Temperature will have geometric and volumetric effects on the material, and hence turn into a mechanical effect- and finally electrical signal is outcome.
Forget the fuel pump switch and the T.H.A, the Mass air flow signal is Vs; Vb; Vc; E2. Where Vs is supply of 12V, Vc is input signal from ECU of 3-5V; and Vs is output signal that will NEVER/SHOULDN'T be greater than the ECU's input signal. But like I said, this circuit can run fine with only 5V to Vc. We can see that 5V from Vc can easily make it to earth, with a variable resistor in it's way which will act like 2 resistors with it's adjustable needle pointing out for the signal output. Which acts kind of like a voltage divider circuit with 2 resistors and an output leads away between those 2 resistors (Vs).
This variable resistor is configured to be Maximum at Vane CLOSED position, so when Vc of 5V comes through the rheostat to Vs we will have minimum signal, because most of the voltage drop is for the BIG selected resistant part on the rheostat, only a little comes out for example 1.26V.
As the vane opens wider(got pushed in by more air) the rheostat becomes smaller, hence Vs leads a bigger output signal, just like how a voltage divider works as we change the value of its resistors. And of course, we can't have a voltage divider where all the supply comes out the output terminal while none goes to the following resistor to earth, that would make NO SENSE of a voltage divider anymore. That's the reason why the signal must not be or be bigger than the ECU input. But, when you have Vb hooked with the 12V+ battery, 5.08V(actual @ max open position) might as well be what you have.
Current is not a concern in this type of circuit, where only Voltage and Resistance matter. So we can test the operation of this VANE MAFS by 2 ways through resistance meter check and available voltage check.
Put the black lead on the E2, @ Vs varied between 80-900 Ohms in total and this is fairly between specification. This only tells me that the rheostat is in the voltage divider range in order to have a desired voltage signal. E2-Vb & E2-Vc both possess the same amount of resistance ,this tells me that the maximum resistance of the rheostat and the Vb resistor are similar.
It behave seemingly like exponential. But as Ohm's law applies: V=IxR, this relationship should be linear and directly proportional because vane angle represents proportions of the rheostat being selected.
Fuel pump switch: a smart mechanical link between the rheostat's needle @ zero angle position and the fuel pump switch.
Disadvantages:
There are several types of air flow device besides this vane they are Hotwire Mass air flow sensor, Karman Vortex air flow sensor. And the most common is hotwire mass airflow sensor. The reason this Vane device is not called "sensor" because it is actually a meter, which convert analog mechanical movement into electrical signal. Other sensors convert heat energy into voltage signal, or photographic changes into voltage signal, which are more likely to be called "sensor" than "meter".
The Vane type mass airflow meter consists of a moving mechanical flap, hence the weight and recoil force of the spring setup exert on the flap can restrict the flow of air, hence restrict performance.
In consistent and frequent operation of the intake air, a complex of mechanical components will eventually worn out, and dirt deposits on components. Which may lead to hard starting when the engine needs the vane to actually opens up a little bit when throttle is not depressed.
Beside, the spring composition can be out of service too, which will terminate all the voltage output function of this vane type mass airflow meter.
Comparing to the Hotwire, the vane MAF takes more room and weights much more heavier than a tube of plastic with some wire in it, hence replacing a vane with a hotwire is a much better choice. In fact, most cars use hotwire MAF sensor.
-Large & heavy
-Performance restricting=> lessen fuel economy
-Not as reliable as the hotwire MAFS
-Not as accurate as the hotwire MAFS
I truly like to reading your post. Thank you so much for taking the time to share such a nice information.
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