[dn]

Bohdan Bodnar wrote:

> GM and Chrysler MAP sensors have an output which is roughly between 0.1 and
> 4.9 volts. 

This is to allow for mfg. tolerances to gurantee that any given unit will
be within the 0-5V input range of the a/d converter.  The zero offset also
provides a little headroom for noise immunity.

> At atmospheric pressure, a GM or Chrysler MAP sensor designed for a self 
> aspirated engine will output around 4.9 volts whereas a sensor designed
> for a supercharged engine will output around 2.5 volts.  

This makes sense if you think in terms of absolute pressure instead of vacuum.
A 0 - 30 PSIA sensor would read 1/2 scale at 1 Atm.  Less than this is vacuum
more than this is boost.  A normally aspirated engine would only require the 
0 - 14.7 PSIA half of this range.

> Ford's MAP sensors (and BMAP sensors) output a variable frequency.  At 
> atmospheric pressure, the frequency will be between 155 and 159 Hz.
> About a year ago I posted a table which gave output frequency vs. pressure 
> for a Ford MAP sensor.  

Would you kindly email this to me, if you still have it kicking around? 
Actually, post it to DIY_EFI, there are probably more people who would like
to see it.

regards
dn



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