5v or 12v for MAF?

[ryan_george]

In the process of my MAF swap, but I've a question. ('98 M3 siemens MAF).
To power the MAF, do I use the 5v that the AFM used, or another switched 12v?
I've already wired the MAF connector in parallel with the AFM, and I used the 5v source. Plugged it in, but I couldn't get any readings from it. The output was stuck at 0.08v. I believe I've got it wired correctly (1 - ground, 2 - signal, 3 - power, 4 - unused), but should I try the 12v anyways?
I'm not sure of the outputs of this MAF, but the AFM outputs 0 - 5v to the ECU, so I would assume I should use the 5v so I get a similar output.

[Digitalwave]

The outputs of the MAF and AFM are not comparable. That's why you have to use a piggyback ECU to convert the signals into 0-5v like the AFM uses.

[ryan_george]

Yeah, I'm aware. I'm using the SMT6.

[Digitalwave]

Re: 5v or 12v for MAF?

I'm not sure of the outputs of this MAF, but the AFM outputs 0 - 5v to the ECU, so I would assume I should use the 5v so I get a similar output.

This statement confused me.

[ryan_george]

Re: 5v or 12v for MAF?

I'm not sure of the outputs of this MAF, but the AFM outputs 0 - 5v to the ECU, so I would assume I should use the 5v so I get a similar output.

This statement confused me.

The AFM is powered by 5v, and it's output is between 0 and 5v. This means that at full load, there is very little resistance in the circuit.
If the MAF has a very small resistance at full load, then I should power it with the 5v, thus giving me the 0-5v range I need. But I don't know the specifics about the circuitry in the MAF, so I'm not sure what its resistance will be like at full load. This is where I'm unsure.

I don't really know if that cleared it up at all...

[bmwman91]

With a MAF that new make sure it gives analog output & not digital. With a reading of .08V that sounds a little like what you would be reading on a DMM from a digital/square wave output. Were you reading the voltage on a DMM or from the SMT6?

[ryan_george]

With a MAF that new make sure it gives analog output & not digital. With a reading of .08V that sounds a little like what you would be reading on a DMM from a digital/square wave output. Were you reading the voltage on a DMM or from the SMT6?

I was reading it from the SMT6. People have used these MAFs before, so I would assume it to have an analog signal.