Transformers

[garfield at pilgrimhouse.com]

On Fri, 29 May 1998 01:50:56 -0600, Shannen Durphey <shannen at mcn.net>
wrote:

>Here's what I've noticed.  In DIS systems, if one plug wire
>burns open, other plug often fires anyway.

Oh, goodie. I was hoping this would come up, cuz I too was kinda
surprised to read about this. Lest this sound like some wild
theory/speculation, lemme read for you from a GM document I got from one
of our illustrious group members, who also went mum some time ago, due
to excessive frustration levels.

"It is possible in a no-load condition, for one plug to fire even though
the spark plug lead from the same DIS coil is disconnected from the
other spark plug. The disconnected spark plug lead acts as one plate of
a capacitor, with the engine being the other plate. The two 'capacitor
plates' are charged as a current surge (the spark) jumps across the gap
of the connected spark plug. The 'plates' are then discharged as the
secondary energy is dissipated in an oscillating current across the gap
of the spark plug still connected."

So what they're saying is that there's enough stray capacitance from the
dangling HV lead not connected to a plug, and because the frequency
components of this HV spike are also very high, you have a complete "AC"
circuit for the secondary, even though you don't have a plug there to
fire on one of the two ends. Hence, even with one of the two plugs
disconnected the other plug may fire.

>Have seen integral type HEI run with no ground for the
>secondary. Must find a ground through the module, because
>that's usually what I end up replacing first. Then coil is
>bad and I find ground strap is missing. 

Likely same phenom as above. But it's REALLY also true that running any
HEI or DIS system without a load on the secondary (namely, plugs), can
cause the HV on the secondary to REALLY skyrocket, AND cause large
ringing in the primary, which might be what is damaging the module, but
yup, the HV finding a sneak path through insulation into the primary
circuit is ALSO a very real possibility.

Gar