Dwell Control

[G. Scott Ponton]

Ok correct me if I'm wrong but I don't think the TY/SY system is a HEI. I
don't remember seeing a distributor in any of the Buick turbo apps I have
ever looked at. They have a cam sensor which generates a signal to the ECM.
The ECM conditions the signal then sends it back to the ignition system. I
don't remember exactly what the signal looks like though. It has been
several years since I had to check one for no function. I will go through my
notes tomorrow when I get to work and see if I can find it.
    The dwell aspect is also a moot point. In distributor apps with one coil
the dwell becomes important , as someone else has already pointed out, but
in a DIS system with multiple coils the dwell time is depentant on the time
it take to charge the coil fully between cycles. So on DIS systems the coils
can be allowed to charge for as long as it takes to get another signal to
fire. This may amount to 90 degrees on and 8 cyl. engine or 120 on a six
with 3 coils. I have never checked to see if the coils have a variable dwell
period. It makes more sense that they would set the dwell so that at max
engine speed the coils have the proper time needed to charge and leave it
fixed across the rest of the RPM band. This way the circiutry and
programming need can be minumized.
    Last bit of input. I have no idea if this is correct either. Most of the
EST systems I have worked with, run from the point of view of the max timing
is part of the EST and depending on the signal from the ECM it retards the
timing from this point. Suppose the value you see as the initial timing
value is a max value calculated from the crank sensor. Then the values in
the timing tables would represent the amount of retart from the max value.
This could possibly explain the lost of timing control  when the value is
changed. In a 6+1 system it would be the pulse after the odd one which would
indicate cylinder # 1.  Also I was under the impression that the 2.8/3.0 v6
actuall only sent 4 signals per rev. 3 at 120 degrees from each other and 1
odd one some 10 or 15 degrees  out of pattern.
    Once again this is only conjecture at this time as I haven't spent any
real time looking at the signals from this point of view. Normally I am only
interested in getting the customers vehicle running again.
    I will look through my notes in the morn and see if I can get any usable
info.

Scott