Do I need an Air Flow Meter?

[James Montebello]

On Mon, 4 Dec 2000, Bruce Plecan wrote:

> 
>> You mention that I would probably need a sensor for barometric  pressure,
>> air temp, and RPM.  The stock AirFlow Meter doesn't have any of this.
> 
> Doesn't have to, it's figuring mass

Just picking a nit, but the Bosch "flapper-type" airflow meters (as the
original poster was asking about) do have an air temperature sensor built
into them, and provide it along with the flapper position.  The later
"hot-wire" type of airflow meters are themselves temperature sensitive,
so ambient temperature is accounted for automatically.

To the first poster, if you know airflow correctly, you don't need to
know engine speed.  Bosch K-Jet doesn't have an engine speed input.
It does usually have some input related to the throttle position
(depending on the type, this is either a MAP reference, or a TPS).


> Just too hard in my opion to get enough resolution in using just a MAP to 
> do it. Hard to tell at times if your actually doing what ya seem to be 
> doing because of Baro.

I would think that MAP would be directly related to barometric pressure,
since lower barometric would automatically mean lower MAP for otherwise
identical conditions.  Since you want less fuel at altitude, and you'd
get a lower MAP value at altitude, a fuel curve matched to MAP, with
throttle compensation for acceleration, would be adequate.


It's funny how many people are suddenly showing up wanting to replace
airflow meters with MAP output.  I'd thought about doing exactly the
same thing to by L-Jet equipped Alfa.  

james montebello

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