555 EFI

[thergen at svn.net]

Bruce,

Are you thinking of a string of one-shots and using a varying
voltage on
the control pins to vary the output pulse width?  If you're already going
to be using op-amps to scale the output of the sensors, you could probably
add/subtract the outputs of multiple op-amps together through resistors
and run that into the control voltage pin of a smaller number of 555s.

Since there's not 'learning' ability, the circuit might be very
engine/sensor specific.  Trying to apply it to an engine with a slightly
different offset in the TPS or MAP sensors compared to the original
engine/sensor combo it was tuned to might not work very well (without
retuning that is). The same could probably be said for other fi
controllers without feedback. 

Use capacitors with good temperature coefficients.  X7R caps would be
preferable to Z5U caps.

Good Luck! (meant in an encouraging way)
Tom

On Fri, 15 Jan 1999, Bruce Plecan wrote:

> 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  
>