Dwell Control

[Tedscj at aol.com]

In a message dated 4/12/99 1:25:57 AM Eastern Daylight Time, 
gscottp at ix.netcom.com writes:

> 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.

The Sy(clone) Ty(phoon) is definitely HEI with a distributor.

> 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.

I have been considering this point.  I have been playing around with the 
maxrtrd and maxadvn values but haven't had any luck.  I believe it must have 
something to do with these, though.  I think you might be right, here.

> 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.

Yes, you are right.  Every other pulse is ignored by the DIS module (except 
the synch pulse.)  SO the first pulse after the synch pulse is ignored and 
then every other one after that (until it senses another synch pulse.)

>      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
>  
>  

Ted