555 EFI competition

[Garfield Willis]

On Fri, 30 Jun 2000 13:04:50 -0500, bcroe at juno.com wrote:

>The whole thing is done with OP AMP type analog circuits.  The
>basic fuel curve is a simple straight line of manifold absolute
>pressure vs pulse width.  For Wide Open Throttle a second 
>richer line overrides the other.  I have reverse engineered the 
>entire thing with detailed drawings of the circuit and explanations 
>of how each section works (except that J-K Flip Flop).  This info
>is free to anybody by snail mail; I think someone has also
>scanned it for E transfer

This *wonderful* relic should truly be uploaded to the FTP site if at
all possible. It would most certainly "win" General von Munchausen's
farsical competition, hand's down, 555 or not. If no one has a scan,
I'll get a copy from BruceR if he's willin, and put it up thar meself.

BTW, the J-K FF is a pretty straight-forward device if you want me to
explain it to you, Bruce (and indeed is probably the storage device for
the 'equivalent of a 555' in the Caddy design), so you can round out
your historical package of notes and drawings, and get everything nailed
down. And PLEASE don't anyone think I'm being sarcastic here; we (our XA
group) have our own form of this, yes using a 555 for the PWM in fact,
that we use on eXperiment Aircraft engines (yeah, I can just hear
someone saying, "uh oh, there he goes again" :), and it isn't
closed-loop either (100LL and O2 sensors are somewhat problematic, but
the new unleaded Avgas is coming, so we may soon be able to close the
loop). That's cuz you don't need pump shots or other enrichment
transients in an aircraft application, and since everyone's used to
tuning mix manually via EGT, a linear fueling curve is PERFECTLY
adequate for us anyway, as long as a manual trim is provided for fine
tuning.

The system we built, which we called "KEFI - Kiss EFI", goes along with
a DIS IGN system, whose fixed advance curve ALSO is perfectly adequate
for aviation, since vacuum advance isn't required. We modelled our XA
system after a continuous FI system build by Continental Motors in the
'40s!

>There is a mechanical switch on the throttle which feeds back 
>21pulses as the throttle opens so the injectors can fire extra 
>enrichment pulses.  It also indicates max or min throttle to the 
>ECU.  There is not a variable resistor to feed back a voltage

Tell us what you can about "felt driveability". Was it acceptible in
your opinion? Had to be pretty close, I warrant, in order to deploy the
cars in the first place. Please say more about how they drove.
Fascinating.

>These units are fairly common in junk yard 76-79 Cad Sevilles
>and I have modified the pulse width for engines other than the
>stock 350.  But the possibilities are limited with a straight line
>fuel curve and no feedback loops.

Maybe so, but I still think this ought to be a prized relic in any
DIY_EFI "smithsonian", as an illustration of just how far you can get
with the basics.

Gar


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