MAP calculations?

[Dave Zug]

If I wasn't a 'maf zeolet' (someone elses words) I might have a better
answer, but my answers usually get someone else interested enough to correct
/ add to mine ;-) so here goes.

well in lueu of NO responces....

My MAP experience (2 bar) had me looking at the RAW MAP VALUE cell,
multiplying by 2, dividing by 100 which gave me voltage on the sensor.  ie
250 = 5.0 volts which is 200 kpa absolute (the max for the sensor)  I had
assumed the MAP sensor was linear therefore 2.5V = 100 kpa (absolute) and 0V
= 0 Kpa absolute.  If you want PSI.. 200 KPA absolute is 100 KPA over
atmosphere, is 14.7 PSI (or 14.5, depending on who makes the best argument
this month, and how technical you want to get)  0 Kpa is 14.7 PSI of Vacuum.
To apply this to a 1-bar, 100 KPA is a MAP value of 250 is 0 PSI relative to
atmosphere, and 0 Kpa is -14.7 PSI (-28 in Hg or nearly a perfect vacuum -
ie closed throttle plate)

<asbestos suit on>  Input from others is on the way I'm sure ;-) I really
never studied the formulas. I'm putting my ignorance out here in hopes it
will benefit you. The formula indicates the MAP sensor has a base of 10.3,
NOT zero so my rough guestimates are off. It is also the formula for the 1
bar... so watch out in my post.. lotsa 2 bar stuff there.

you are running rich at idle - need to  decrease VE in those areas by the
proportion of 128 that the cells are off. ie ((128 / 110) * current VE
value) will get you close (lil guys?).

Elves are working on my MAP upgrade even as I sabotage their efforts..
eventually I'll be cornfusing the MAP people with my responces too ;-)



----- Original Message -----
From: Reid Bishop <rbish at ibm.net>
To: <gmecm at diy-efi.org>
Sent: Friday, October 06, 2000 8:38 PM
Subject: MAP calculations?


> I'll ask this question once again, having not heard an answer before.
>
> When reading the MAP voltage output on a 7747 ALDL datastream, how does
one
> convert it to actual MAP pressure?  The only source I have says this:
>
> MAP kpa = MAP(AD)/2.706 + 10.3
>
> Is this correct?
>
> Here at 6300 feet, my 4.3 idles at about 37kpa, with the IAC running
38-42.
> I still am showing 110 BLM's at idle, and I am having trouble getting it
> leaned down some more.  I'm just wondering if I am adjusting the correct
VE
> cell.
>
>
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