a MAF too small

[Jason Haines]

Regarding the minimum flow rates, you do need to make sure you are not at
the bottom of the scale at warmed up idle but we have used this technique
(the two MAF method) as have other companies when nothing else would work
(I have even seen a GM development vehicle with two MAFs but only one
connected but I was told they had also doubled the MAF g/s to frequency
table in the calibration - in the example described with the 1986 to 1989
that is not possible the table is already at the maximum of 255 g/s and
with the voltage type MAF the range is fixed 0 to 5 volts unlike the
frequency type that often have much more range than the vehicle ever uses).

On modified engines you are usually idling at a higher g/s than stock
(especially if you have a larger engine and a higher than stock idle speed)
so you can usually half the scale at still not have gone below the bottom
of the table. One thing to do on voltage based systems would be to check
your warmed up idle voltage from the MAF - stock is 0.5 to 0.7 volts. If
you are higher than this on a modified engine then you have some room left
in the table. Keep in mind a lot of the calibrations are designed for very
low idle speeds (525 rpm in some cases).

Finding a larger (higher flow range - not restriction) 0 to 5 Vdc Bosch
type meter has not been easy either. It seems that in those cases where
higher ranges were needed, some of the OEMs also went to two MAFs (Nissan
Skyline, BMW M5, Mercedes V12 etc...).

So who feels like making an analog averaging circuit for two 0 to 5 Vdc
signals? You could leave the burn off circuit attached to just one MAF or
make it operate both MAFs if you wanted.  8-)  (What would the time delay
in such a circuit be?)



Jason


At 02:24 PM 7/23/99 -0500, you wrote:
>I'd look real close at what the min rate the MAF will accurately sense 
>before, running out and buying injectors to try this.
>  I thought the Hacs showed a min, and max frquency?.
>Bruce
>
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>>At 01:18 AM 7/22/99 -0800, you wrote:
>>>Isn't the problem not that your maxing the MAF sensor, but that you are
>>>maxing the computers internal airflow variable at 255 g/s?  It's a
>>>frequency MAF, right?
>>>
>>
>>The 1986 to 1989 Corvette, Camaro and Firebird use a Bosch MAF sensor that
>>is a 0 to 5 Vdc sensor not a frequency type sensor (like that used on the
>>1994 and newer Corvette, Camaro and Firebird).
>>
>>One thing you can try is using two stock MAF's is parallel with the ECU
>>only connected to one MAF (but air flowing through both) and then using an
>>injector twice the size the computer thinks it is. It is VERY important to
>>design the air intake so that the same air flow goes to both MAF's - test
>>it on a flow bench with a voltmeter if possible.
>>
>>
>>Jason
>>
>>
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