Bosch AFM testing

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Bosch AFM testing

Post by Guest » Fri Dec 12, 2008 12:29 pm

Can anybody help me with a testing procedure for the latest air flow sensors as fitted to later vauxhalls Vectra c and astra h. I have come accross 3 cars recently where I have measured a very fast switching square wave pattern on the pin which is normally the output voltage.
Sorry I don't know how to attatch my capture, the frequency of the waveform seems to change with engine load but the duty cycle remains about 50 percent.
Could anybody help me with a testing procedure, should I be measuring current flow?


Any help would be very much appreciated
Thanks John

chris1234
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Post by chris1234 » Fri Dec 12, 2008 10:20 pm

I think you have a Bosch HFM6. The air-mass-information is coded in the frequency and the air-temperature is coded in the duty cycle.

I have an Excel-file for a HFM 6, that you can download here. It's in German, but maybe it's helpfull.

Luftmasse = Air mass
Ansauglufttemperatur = Air temperature
Pulsweite = Duty cycle
Luftvolumen = Air volume

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Carl Grotti
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Post by Carl Grotti » Sat Dec 13, 2008 10:48 pm

Hello John,

Testing "Air Flow Meters" or "Mass Air Flow" sensors can be tricky when they are frequency based instead of a proportional analog one. It can be done fairly easy enough though using PicoScope.

You can do this a few different ways. Utilizing the advanced triggering is one way. Myself, if I were to use a scope to do this, then I would trigger off of the TPS. This would give you a relationship of when the throttle was snapped and the corresponding frequency with the cursors in place.

Another way is to simply use a PGM or a GMM that graphs frequency over time.

Most of the time this can be nailed down with a scanner. Not always though. Out of curiosity sake, what are you using for a scanner?

Guest

Post by Guest » Mon Dec 15, 2008 7:22 pm

Thanks for your replies. I will have a play with the next one I get in and see how I can best display the frequency.
Carl, I am usind a sykes pickavant ACR 4 scanner. it's very basic and unfortunately cannot graph any of the component data.

Many thanks
John

Dave Hill
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Post by Dave Hill » Mon Feb 16, 2009 9:08 pm

Carl Grotti wrote: Another way is to simply use a PGM or a GMM that graphs frequency over time.
I am very interested in developing a useful method of testing these digital MAF sensors. I have to confess Carl that I don't understand the abbreviations that you used in your reply.

Recently I put it to Matt (At Pico) that it would be a cool addition for Pico, if it were possible to graph the frequency over time, in a manner that allowed us to see a plot or simulated signal. This would be very useful for comparing the digital MAF output against the Oxygen sensor, so that effective study of closed loop control can be made.

I don't know if this is a realistic request, but I think it would be a real bonus for Pico.

Cheers

Dave Hill

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Carl Grotti
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Post by Carl Grotti » Tue Feb 17, 2009 6:22 pm

Hi Dave,
I have to confess Carl that I don't understand the abbreviations that you used in your reply.
Sorry about that.

PGM = Power Graphing Meter

GMM = Graphing Multi Meter

Here is the one I use.

http://buy1.snapon.com/products/diagnos ... ir=catalog

There shouldn't be much trouble finding a used one at a very low price since the V-Pro replaced it.

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