TinkerMan wrote:
>
>
> Thanks!
> what's "psig" (sp?)?
>

psig means pounds per square inch gauge.  This is what most people mean
when speaking of the pressure in tires, fuel lines, cooling systems,
etc.

The other approach is  "psia" meaning psi absolute, which would be about
14.7 psi more because it includes the air pressure around us all the
time, at sea level on the average about 14.7 psi, 101 kPa, 1 bar or atm,
or 760 mm mercury or torr.  The computer in a fuel injection system
wants to know the absolute pressure in the intake manifold, hence the
term MAP sensor, manifold absolute pressure.
  Since you can't have less pressure than a complete vacuum, psia
readings are never negative.  Complete vacuum on the psig scale could be
called -14.7, but since vacuum is usually measured in inches of mercury
in automotive work, you see it as 30 in. on an AC gauge.
  Sorry, I'm a physics and chemistry teacher, just can't help myself...

Larry A.