efi555

[George M. Dailey]

At 01:50 PM 1/27/96 MDT, Darrell A. Norquay wrote:

>And so it begins.  The questions, I mean.  
>I'll try not to pester you too much with this, but it sounds
>almost too good to be true.  I'll be hunting down parts over the
>next few weeks, and I'll post my results to the list if anyone's
>interested.  Thanks in advance for any info.

Darrell A. Norquay



Darrel,  before you start your holy pilgrimage for discrete electronics,
let's kick one more idea around.  Back in '87 or so,  I built a 555 based FI
control unit with only one variable resistor controlling the pulse width.
The timer was configured in a monostable mode to fire the injector twice per
revolution. On the bench, the electronics worked like a charm. I never got
around to testing the electronics on an engine with actual injectors.  I
started reading about how the GM EFI systems worked and those OEM parts were
starting to show up in the salvage yards in large volumes at low prices.  I
convinced myself  that OEM was the way to go.

I started having the same questions that are circulating around now about
the 555.
If I were still interested in building an EFI control unit from scratch.  I
would seriously consider the Basic Stamp microcontroller by Parallax.  With
8 i/o's, you would have a lot more flexibility than the 555. Imagine:

i/o 1 = injector driver
i/o2 =  rpm input (this could be a permissive to prevent that theoretical
engine run away)
    3 =  MAP input
    4 =  MAF input
    5 =  you get the idea....

It's a lot easier to connect the Stamp to your PC and modify the program,
than to fiddle with resisters, capacitors, and other discrete devices.  I
haven't used the stamp yet, but it seems ideal for this application.  They
are priced around $29 - $39 (I THINK). Check out their web page.  One more
thing, the Stamp might work best in the astable mode.  I'm not sure if it
would be fast enough for 'real time' reactions of less than 20 ms.  But I
could be wrong.

Keep us posted and good luck.

George M. Dailey   gmd at tecinfo.com