Dwell control vs timing control

[Tedscj at aol.com]

In a message dated 3/4/99 6:24:52 PM Eastern Standard Time, nacelp at bright.net
writes:

> gm specific
>  I been thinking way to much on this, but, I'll stick my head out again, and
>  say
>  what your reading in the prom is timing corrections, and the stuff for
being
>  a cylinder late in the computations.
>    If the dwell controll, was in the prom, then disconnecting the
distributor
>  from
>  the ecm would stop the engine from running.  So the dwell control is in the
>  module.
>    So every thing in the prom would look the same from Dissy to DIS.  Just
>  a matter of when the timing starts, as set by est signal.
>  Thoughts anyone?.
>  Bruce
>  

According to the P4 Document, the module controls dwell in EST BYPSS mode, and
the ECM controls dwell in EST mode.  I know this is how Ford does it too,
according to some books I've read.  Also, you can see the dwell in the EST
signal, and the GM EST signal looks just like the Ford SPOUT signal that I've
seen in some books...Dwell control and all.  In short, based on everything
I've read and seen, I am about 99% certain that the ECM controls dwell under
NORMAL operating conditions.

But you are absolutely right that the EST signal for a DIS and a Dissy are
identical, it is just the TIMING that is off.
When I use the Dissy prom with my DIS, every thing is about 60 degrees too far
advanced.  What I don't understand is why when I changed the KREANGL (Spark
Reference Angle) in the SyTy .bin, absolutely NOTHING happens.
According to the P4 Document, KREFANGL is subtracted from the total timing
computed by the ECM.  This should fix the problem but it doesn't.  I can
detect no changes in spark angle no matter what value I put in there.  It
seems to have no effect whatsoever.

I guess this is why someone simply inverted the Reference Pulse  Because there
is no other way I can find to bring the timing back to where it should be.
There should be no reason to invert the EST signal.  It's the Reference Pulse
that is off.  If you get the ECM to read the Rising Edge instead of the
Falling edge (by inverting the signal) then everything should work alot
better.  Maybe still a few degrees off, but not 60 degrees off!

In short, Bruce, you were right that the solution is to invert the signal
(Reference Pulse).  I just wanted to try a few things in the Prom first, but
nothing worked.

Which brings me to a question:  How do you build a circuit that inverts a
signal? :)

Ted