555 EFI

[Bruce Plecan]

I've been thinking about a simple EFI using a string of 555s.
Just like the "Normal" math would be, ie first 555, base pulse,
second Coolant temp correction, third MAP, and so on for like
6+ 555 all in series.  Trouble is this gets me, an addition of
correction factors, instead of multipling them, is this a major
problem?.  I realize this ain't gonna be as good as a oem,
ecm, but would like to get fairly close.
  I'm looking to keep this as much as an entry level thing, meaning
nothing but 555s, op-amps, and a final drive.  
  On a related note, does anyone know if the gm ecms use a 
standard "pinout" for the resistors in the netres?.  Is the netres
only for full limp home mode, meaning it goes to fixed timing?.
Any thoughts appreciated.
Cheers
Bruce