Homebrew additional injector controller - need suggestions!

[Askren, David]

I am attempting to design a build an additional injector controller to add 2
additional injectors to my 1992 Ford Probe GT.  The car has the Mazda 2.2L
Turbo engine.  I would like to use a map sensor that could support 21 psi,
so a 2.5 bar map would be ideal, correct?  Or should I use a 3 bar?  Does
the 3 bar map support 1.5 or 2 bar above atmospheric?  What does a 3 bar MAP
read at 0 psi?  Is it 2.5 volts?  Should my controller fire the injectors
simultaneously on each cylinder fire (they will be in the intake tract
between the intercooler and throttle body)?  I would like to be able to set
the boost level at which the injectors begin to fire, say 9 psi, and have
them ramp up the duty cycle untill 21 psi, my desired max boost level. They
will fire based a signal from the cam position sensor.  Any idea what the
output of the CPS looks like?  From what I can imagine, I shouldn't need to
use a processor, as discrete should work fine.  I will draw it up and put it
on a page tommorow.  Suggestions very welcome!
Dave