EST observations (kinda long)

[Tedscj at aol.com]

In a message dated 2/23/99 9:51:47 AM Eastern Standard Time,
shannen at grolen.com writes:

> For some reason, I missed the earlier post.  What is this about?
>  Shannen

I'll repost it.
I'm basically trying to figure out exactly how the ECM signals the DIS (or
HEI) Module for Dwell and Ignition Advance.



First, This info pertains to the DIS module as fitted to GM "W" V6 engines.
I am trying to find the differences between how this module communicates with
the ECM (and appropriate .bin) and how an HEI module works with the ECM (and
appropriate .bin) so as to find a way to interchange the two with the Sy/Ty
.bins.

What I did:  Since I don't have an oscilliscope, I recorded the pulses, both
generated and recieved by the DIS module, with a tape recorder and analyzed
the recordings with sound editing software.  I got the idea from the
"STREETDYNO".  I was tape recording the output to the tachometer to use this
in the StreetDyno and decided "why not record some other things and see what
they look like?"

What I recorded:  The RPM Reference pulse output signal from the DIS module to
the ECM (purple/white wire) and the EST (electric spark timing)(white wire)
from the ECM to the DIS Module.

What I saw:  heres a JPG of it since my text art doesn't work 

http://members.aol.com/tedscj/EST.JPG
Top half of image


You see that these are all equally spaced.  The P4 document states the the ECM
looks for the 'falling edge' to determine a reference pulse.  I have read and
heard that the difference between an HEI module and DIS module is that this
signal is inverted.  So maybe a DIS .bin looks for a 'rising edge'?  Either
way it can't be much of a problem since even an inverted signal has a 'falling
edge'.  You migh just have to adjust the base timing to make up for the pulse
displacement caused by the inversion.

and the EST signal from ECM to module:

http://members.aol.com/tedscj/EST.JPG
bottum half of image


Next come the assumptions:
First, I am assuming the upward spikes represent the 'rising edges' and the
downward spikes represent the 'falling edges' that you would see on a scope.

ex.

____I____I____I____I   on my tape recorder
 I          I      I       I
would be:
-]__[-]__[-]__[-]__[   on a scope

Does this make sense?


Second set of assumptions about the EST Signal and Dwell:
First, The P4 document states many times that the ECM controls Dwell and Spark
advance Timing through the EST signal.  I am assuming that there is a
theoretically perfect amount of time for a coil 'ramp up' at a given voltage.
Not to much so it won't over heat and not to little so it can't accumulate
enough 'juice'.  Dwell time with a distributer would be a compromise between
enough time to ramp up and enough time to fully discharge.  This compromise
would be different at different RPMs.  With a DIS system, there would be a lot
less compromise because of the additional time available due to the 'time
sharing' of the multiple coils.  Therefore you could basically set the dwell
for optimum and leave it, up to a higher point in the RPM range than with a
distributor.
Am I correct?

Looking at the EST signals I recorded I can see only one way that it can
control timing AND dwell.

@1200 RPM

[------]___[------]___[ etc.
11msec.  6   11     6msec.

and @3000 RPM

[-]___[-]___[-]___[-]___  etc.
1.5 5 1.5 5 1.5 5 1.5 5msec.

Basically, when it goes LOW it is ALWAYS around 5 or 6 milliseconds, at least
up to 3000 RPM.  (I'll record at a higher RPM tomorrow.)  I am assuming this
is the commanded dwell time.  I am also assuming that when it goes HIGH, that
this is the command to fire the coil.

Of course, the compromise btween dwell and ignition time would be completely
different with a distributor.  With the DIS, the ECM doesn't have to worry
about allowing enough fire time because the coil circuit can remain closed
while the next coil is ramping up.  This scenario would help explain why DIS
.bins would not work with distributors.  The dwell timing is all off.  There
is not enough time left for the coil to fully discharge.
The other problem could be that this signal is also inverted as compared to an
HEI module.  In other words, an HEI module might want to see it go HIGH for
commanded dwell time and see it go LOW to command ignition.

Of course there is more, but this is enough for one post!

Does this sound right to you?  Does anybody know if this is right?  Am I
completely bonkers?

ANY feed back would be appreciated.  ESPECIALLY on dwell theory, since I
really don't know that much and am doing alot of assuming.  AND if anyone
knows what the EST output to an HEI module looks like.


Ted