Yup, measuring air flow/resistance is the main part of my research.

But, collection the data on the variations in AFMs is why I am wanting
this data. These variations are the differences in the AFM types
themselves, as well as aging and other things. But, important data points.

Conventional wisdom says that a TPS with MAP and IAT is the solution.
Those inputs going into a microcontroller that would generate the
appropriate output for the stock ECU would solve the problem. But, that's
almost as much hardware (and cost) needed to install a Megasquirt.

I am trying to find an analog solution. It may not be possible, but it's
an interesting project.

Jon

On Thu, 16 Nov 2006, Dennis Haynes wrote:

> The modern replacement for the AFM is known as a Mass Air Flow Sensor.
> Instead of a flap it uses a heated wire and the circuitry generates a
> voltage signal instead of changing the resistance. The main advantage is
> reduced inlet restriction and signal relates flow and density, hence, the
> term mass.
>
> What are you really trying to gain? I doubt you can measure the power
> increase on a water boxer and once the engine goes into closed loop
> operation, the O2 sensor is the real driver for mixture control. In my
> experience, I have actually found 3 bad AFM, 2 on the 1.9 and 1 2.1. They
> were all opened and tampered with.
>
> The data you really need is the voltage at various air flows. If you have an
> open one and observe it with the engine running, you will find that it never
> fully opens nor closes. It will move more with throttle opening than engine
> rpm. The data points will need to be collected under varying loads. It may
> be easier to replace it with a modified throttle position sensor and
> circuit.
>
> Dennis
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
> jon
> Sent: Thursday, November 16, 2006 5:58 PM
> To: vanagon@GERRY.VANAGON.COM
> Subject: AFM Data Requested
>
> I am deep in my research to find a "modern" replacement for the AFM. You
> all out there could help me by measuring resistance of your AFM.
>
> There are the data points I need (measured with an ohm meter, engine
> off, AFM unplugged):
>
> 1) Engine off resistance (between pins 2 and 4)
> 2) Idle resistance (you can probably see a spot on the traces were idle
> is)
> 3) Full "open" resistance
> 4) Half "scale" resistance (move wiper to half way on the tracks)
> 5) Vehicle year, type
> 6) Engine year, type (be sure I know if it's not a stock engine, etc)
> 7) Part number from your AFM (important)
>
> This is not something for the faint of heart, so you need to know what you
> are doing. Here is the procedure:
>
> 0) Make sure car is off, battery disconneted for good measure
> 1) Open up "hood"
> 2) Open AFM (black cover is "glued" on)
> 3) Unplug AFM
> 4) Get ohmeter, and connect to AFM pins 2 and 4(ground). A digital ohmeter
> is recommneded.
> 5) Measure the above parameters
> 6) Put everything back together
> 7) Email me the results. ;)
>
> I will post a spreadsheet with my findings.
>
> Thanks,
>
> Jon
>