Dwell Control

[Ward]

Generaly you are correct, but:
1) there are several variant of DIS system
2) The will all run an engine w/o the help of an ECM/PCM, (no programed
spark adv)
3) none of then will run on a single DRP. It is essential that you have a
valid DIS signal from the engine.
4) Most all are "lost" or "wasted" spark systems

Ward


On Fri, 16 Apr 1999 01:09:45 -0500, G. Scott Ponton wrote:

> Back to the problem with using a SY/TY bin with a system designed for
DIS.
> 
>     All of my notes tell me basically the same things. All of the control
> signals between the ECM/PCM and the ignition system are the same between
the
> HEI and DIS style systems. Although there are 2 different variants of the
> DIS system and 2 different HEIs. The differences seem to be the same for
> both systems in that each one has a fuel sync generator of some sort in
> order to work with SPI. In the HEI system there is an aditional hall
effect
> IC built into the distributor which generates the fuel sync info. The DIS
> systems generate this by way of additional circuitry in the ignition
module.
>     In both systems the ignition module is responsible for the entire
> operation of the ignition system. This includes dwell and some minor
amount
> of advance(which is actually more of a variable dwell as RPMs change). It
> (ignition module) is even responsible for determining which coil is fired
in
> a DIS sytem. The ECM does two things in order to interface and control
the
> timing.
>     During cranking and until the ECM senses 400+ RPM it sends a signal
to
> the module to "bypass" the timing control signal from the computer. After
> the engine reaches 400+ RPM it releases the "bypass" signal and takes
over
> timing control. It does this by receiving a reference signal from the
> ignition module which it then modifies and sends back to the ignition
> system. If you connect the reference signal, to the ignition control
signal,
> on both the HEI and DIS systems the ignition system will work totally
> independant of the rest of the engine control system. Provided that the
> bypass signal isn't "active".  The only exception is the opti-spark on
the
> LT engines. This system is more or less parts of both systems used in such
a
> way as to integrate the major part of the ignition operation into the
PCM.
> In this system the module is basically a simple switching device for the
> coil.
>     OK background info finished. On the the other problem. At this point
it
> becomes a magor problem too!! After careful though I think the problem
that
> is occuring has to do with the operational software for the SY/TY ECM.
There
> is something missing in a HEI system. It is missing a sync pulse. It's
not
> needed for the HEI system as the timing and position of the HEI
determines
> which cylinder gets the spark. The DIS system is more or less self
contanted
> BUT.................. a very large BUT here. The computer ( more
conjecture
> on my part from here) probably receives a sync pulse in the reference
signal
> from the ignition module. It then uses this to calculate overall ignition
> timing based on the sync pulse. With the HEI it can just calculate
ignition
> timing per pulse etc. and let the HEI "worry" about which cylinder it is
> firing.
>     Anyone have more input on this or maybe something I have missed??
> 
> Scott
> 
> ASE certified Master
> With Advanced Engine certification.
> 





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