Dwell control vs timing control

[rr]

My understanding of GM's dwell control is that it is in the distributor.
The module measures the coil drive current, once the current reaches
a certain level, the drive is reduced to maintain that level. It would
be
difficult for the ECM to control the max current level through the coil.
The 'ole Kettering systems used a ballest resistor to limit the max
current.

Let's see, Motorola has something on this, hang on a minute...
Weeelll, longer than a minute, but here it is:

"High Energy Ignition Circuits": MC3334P/MCC3334/MCCF3334, in the Linear
and Interface Circuits databook.

Typically peaks at 5.5Amps and holds there until coil fires. For some
reason,
I thought that this is the chip GM uses in their HEI modules. (This is
kinda
like the peak & hold injector drivers, except that the current is held
at max,
not ramped down at hold).

Even the off state duration is controlled to allow full coil discharge.

HTH

BobR

P.S.  Further reading, just before sending this, states (in the
databook),
that this device is designed to serve aftermarket Delco five terminal
ignition applications...

Hmmm, does make you wonder what GM is really doing in the seven terminal
distributors. (I can see some bench work to get the scoop on this one).

>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

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