Mass Air Flow Sensor

h3rk · 12-14-2007, 02:24 AM

Well I have acquired a mass air flow sensor from a 1992 Ford POS on ebay. Ill ask my question first and then post a little of it's application.

This MAF sensor is a 2 element hot wire design, utilizing a thermistor and a platinum wire.
Since I've avoided (so far) having to create my own so far, I wont get too deep into how it works yet.

It has a 4 wire connector, A,B,C,D

A VPWR (switch 12 volts)
B GND
C MAF RTN (MAF signal ground)
D MAF SIG (MAF output signal)

how would I wire this to the brain.

A and B: I would assume would be easy - switched 12V and gnd.

But how would I incorporate into the 3 wire input?

It is a 5 volt (max) signal out:

here is a test for the SIG RTN circuit of the MAF sensor in it's original configuration:

Using a multimeter, check for voltage by backprobing the MAF sensor connector.

With the key ON, and the engine OFF, verify that there is at least 10.5 volts between the VPWR and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

With the key ON, and the engine ON, verify that there is at least 4.5 volts between the SIG and GND terminals of the MAF sensor connector. If voltage is not within specification, check power and ground circuits and repair as necessary.

With the key ON, and the engine ON, check voltage between GND and SIG RTN terminals. Voltage should be approximately 0.34-1.96 volts. If voltage is not within specification, the sensor may be faulty.

h3rk · 12-14-2007, 02:33 AM

I'm kind of thinking that I wont have to use the +5 pin in towards the middle of the board, connect D to the middle (input) and C to the outer,gnd connection. I just want to be sure.

h3rk · 12-16-2007, 05:37 AM

So, I've been staring at my sensor's 2 leads and then at an analog input at my brain, and I think, as much as I want to try it out...

It's not like the pressure sensor where it acts like a variable resistor with only 2 leads.

Any suggestions?

I've got ground (12V) the same for both the sensor, and the brain, but I'm just not sure if that's going to allow me to not use the 5+ on the board, I don't think it will, can I use a transistor as a sort of interface, with a resistor between the +5 and input and the input through a transistor to ground and the signal through it's base? Or would it be easier than that?

Curiosity · 12-16-2007, 02:37 PM

You need a voltage divider (2 resistors). Is the source regulated 12V or ~14.4V with the engine running?

h3rk · 12-16-2007, 04:01 PM

I'm making it up as I go, so the source can come off of regulated 12 or 13.8-14.4(whatever it happens to be at the time).

the sensor acts as a voltage divider itself, but needs 12V supply. In turn it produces it's own 0-5volt.

Are you saying to place a (2 resistor) divider from the sensor's signal output to ground? and tap the brain's input from middle of the divider to ground?

Or put a divider from the input's own +5 supply to ground and then tap the middle of the divider for the input. Then tie the sensor's ground to the input's ground and again tie the sensors signal lead to the middle of the divider?

One of my concerns is that the sensor return on the sensor floats a little off of ground, depending on air temperature. Which makes me think.. I'd also like to exploit that small voltage differential to provide temperature indication.

Here's a picture of my deal (the circuit picture of the MAF is not exactly what I have but very close).

Curiosity · 12-16-2007, 04:15 PM

Oh, sorry. I didn't realize it had 5V out. Just connect the output of the MAF to input of the brain. The thermister is correcting the output so I wouldn't even go through the hassle of trying to get temp off it too.

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