linear EFI

[tom cloud]

>My 2 cents on the simple pot based efi system.  
>
>There is a lot of talk out there, but has any one actually made one of these
>systems?  I have!!.

  [ snip ]

>David J. Doddek                                          |pantera at pobox.com
>Owner SGD Electronics & Development Engr for Caterpillar |h 309 685-7965
>Formula SAE Team Sidewinder 94-95                        |w 309 578-2931
>89 T-bird SC,  69 Fairlane w/SGD EFI                     |fx 217 428-4686
>74 Pantera w/Electromotive Tec-II Twin turbos and Nitros |
>Hey, If you are going to go fast, go REEEAAL FAST.       |
>

David,

I just sent you a "ditto" re your experiences with above-
referenced controller you've done and thought I would elaborate.
I am the reprobate that brought a simple analog or hybrid
analog - digital system into the discussion and have endured
some castigation for my backward ways as well as some agreement.

To answer your question, yes, I have such a system.  It is the
Holley aftermarket EFI.  Has pots for IDLE, MIDRANGE, POWER,
ACCELERATOR PUMP, and CHOKE and that's about it -- with the
exception of a switch on the PCB for small or large block
engine.  It uses only TPS, RPM and engine temp as controller
inputs and uses two injectors for ~650 cfm.  I would like to do
better (thought I'd find a Ford controller, modify the PROM
and retrofit it and EFI manifold, injectors and rails to my
pre-EFI Bronco).

I work with an engineer who designed an EFI for racing jet skis
using hybrid analog / digital (his injector pulse was timed by
a XTAL clock driving a pre-loaded down counter, etc.)  He has also
worked closely with a supercharger manufacturer here in Austin, TX
on FI systems.  He has supported me in thinking that, unless
trying to achieve zero emissions, simplicity (i.e. no micro-controller)
is the best.

I observe that analog, though the building block everything else
is built upon, is not being taught our new engineers.  I guess
I consider myself fortunate to have worked (as a kid) with
"thermionic emission devices" otherwise called vacuum tubes,
analog semiconductors, and then main frames, minis and micro-
computers.

Like most, I love the 'neatness' of digital, but I've learned
from hard knocks that sometimes a relay is preferable to an
SSR (solid state relay) and digital is not necessarily all it's
cracked up to be.

Analog can be unstable (temp and oscillation), but digital has
sampling, aliasing, etc. errors and loss of resolution in conversion
to and from digital.  (Besides if it's too cold or hot for an analog
system, this old boy's staying inside!) The cost of doing a micro-
controller system can be overwhelming, unless you have all the stuff
at work.  One needs a computer, assemblers, dis-assemblers, high speed
oscilloscopes, maybe logic analyzers and ICE's, logic probes, and
lots and lots of printer paper.  (Programmers get rusty zippers and
yellow sneakers, I hear -- just gotta compile one more time.)

One can do the analog design with a 20 MHz scope, a triple output
power supply, and a proto board.  Of course, a copy of Electronic
Workbench or such to do a computer simulation would be helpful.

An advantage of the digital:  it can do data logging and can even
be taught to 'learn' standard system conditions, thereby sort of
self calibrating or adjusting itself -- but this becomes a serious
programming effort.  Been there, done that!  I'm getting old enough
where I'd like to use it in this life.

The digital system could be wire wrapped.  The analog system
could be soldered.  Else one would need to lay out a PCB and get
it etched, drilled and plated.

Well, I've rambled long enough.  All in all, my engineering self really
wants to do this digital, but my 4WD self really wants to just get
to the mountains, and I can't help but believe that the simple hybrid
or pure analog path is 98% as effective as the pure digital with
probably 10% the development time and cost!  (Like you, I've
done systems both ways -- just have never done EFI and have joined
this group to find out more.  The main obstacle I perceived is the
EGO, which appears to be useful but not exact, which really offends
and exasperates my technical side.

SO:  you seem to have done it!!  Please share with us hungry souls
what you've done.

Thanks,
Tom Cloud
Electronics Department
Austin Community College
11928 Stonehollow
Austin, Texas 78758