GM MAF questions...

[Mike Palmer]

Hey all,

I've looked through the archives a bit but didn't find a definitive 
answer to these questions, so I'll try posting directly. I have a 
1994 Ford Probe GT and am looking to replace the cheesy VAF airflow 
sensor used on it with a free-er flowing MAF sensor. Being a former 
GM guy, I bought a used MAF from a 1986 Buick 3.0L (the partnumber on 
the MAF is 25007540). I'm designing an HC11-based controller with an 
adjustable supply to drive the VAF input to the PCM but before I 
proceed too far with the table interpolation logic, I need some help 
finding out:

1) Is there a translation available from Hz to grams/sec available 
for this MAF? At what air temperature is this translation valid?

2) How does ambient air temperature affect the MAF output frequency? 
That is, when air is flowing through it at, say, 50 g/sec, 
will the output frequency be higher for -15C air versus 20C air? If 
so, where abouts can I find the correction curves or factors? I don't 
mind adding an IAT correction algorithm to the controller logic and 
applying corrections to the MAF readings but I'll need the factors.

3) In still air, I've seen about 9Hz and when driven by an 
airhose with good capacity, I saw about 165Hz or so from the MAF. 
What exactly are the limits of the circuit in terms of minimum and 
maximum frequencies? I need this info for diagnostics...

As a related question, does anyone know if IAT sensors used in other 
Mazda cars (i.e. anything with a MECS-II system) can be had 
as discrete parts or are they all buried deep inside the 
airflow sensors as it is in my Probe? I assume the sensors are 
pretty much universal in MECS-II applications...if I'm wrong, can 
somebody let me know? I need to preserve the IAT input to the PCM 
(which originally comes from the iAT embedded in the stock VAF) and 
don't want to try to hack the old one out of the VAF since I may want 
to put it back on someday.


All for now,

Thanks,



- Mike

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1994 Probe GT 
Leather/PMoonroof/5-speed
"You'll laugh, you'll cry, you'll hurl..."

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