Adjustable electronic ignition

[Tommy.Palm at oron.ds.sll.se]

>Just a quick question,
>                                My Holden Commodore runs a Buick 3.8 li=
tre
>V6 and uses a crankshaft sensor for the ignition timing. What I want to=
 do
>is vary the timing, preferably from inside the car. One way to change i=
t,
>although being non-variable, would be to offset the sensor slightly to
>obtain a fixed advance or retard in the timing. What I would prefer how=
ever,
>is to intercept the signal before the ECM, and somehow modify it
>electronically to make it appear that it is advanced slightly. =

>
>Can I do this with a simple capacitance type delay, or would I need to =
use a
>specialised circuit? Also, any ideas what the delay would have to be -
>milliseconds, nanoseconds ? Ideally I would like to have some sort of d=
ash
>mounted box with an adjustable dial or something along those lines.
>
>All input is most appreciated.
>
>Adam Tate.
>[at at multiline.com.au]
>http://www.multiline.com.au/~atate/index.html
>
Hi!

I am not an expert on this specific car but
i have had the same ideas with my home made c-mos ignition system to rep=
lace
the mecanical advance system and have given it some thought.
It`s not very easy. The problem is that you can=B4t control the rpm-depe=
ndent
advance system in your system (i guess) and if you add a fixed timing de=
lay
between the pickup and controlunit it will result in a progressiv advanc=
e in
degrees. A delay of say 0.5ms vill result at 1000rpm in a advace of
60/2*1000=3Dtime between ign pulses/cyl=3D30ms
365/30=3D 12.17deg/ms*0.5 =3D 6.08deg. At 6000 rpm that will be 6*6.08=3D=
36.5 deg. =


That is maby what you  want if the rest of the system was fixed but inst=
ead you
will add that advance also to this. So you see you will probably need a =
rpm
dependend time-delay. It will require 1 or 2 op-amps (for leveldetektion=
 and
shaping) 1 from the dashboard controlled timer and rpm dependent VCO,
controlling the timer. I have done such a combination in a home made fue=
l
ignition once, aiming for cheap circuits. I used 1 NE555 and 1 74LS121 w=
ith
success.
The first thing will of course be to check the output of the pickup to d=
etermin
input and output level of the system.
A hint: tryout the system for temp-dependancy!

All this would be an alternative to a mecanical adjustment of the pickup=
=2E But
that will requier servomotors (or equal)to make a dashboard adjustable t=
iming.

Tommy Palm
[tommy.palm at oron.ds.sll.se]