Date:         Sun, 20 Sep 2015 09:29:02 -0400
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Cause of weak spark?
Comments: To: Angus Gordon <birdworks@gmail.com>
Comments: cc: Andrew Martin <ramblinvan@gmail.com>
In-Reply-To:  <ED36F64C-B03E-4CB2-8FA9-868B5AD2A25F@gmail.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 10:14 PM 9/19/2015, Angus Gordon wrote:
>I'm almost out of troubleshooting time (back to work), but doesn't
>the ECU control the coil power ground? Why the high voltage?

The ECU does basically the same thing that a points-type ignition
does -- it grounds the coil causing current to flow and energy to be
stores as expanded lines of magnetic force.  As the lines expand they
cut the turns of the coil and produce an opposing voltage, so the
current doesn't reach its full value instantly.  When it's time for
the spark the ECU opens the circuit and the stored energy causes the
voltage to instantly rise very high as the collapsing field cuts the
turns of the coil.  This phenomenon is known as inductive kick and
occurs any time you open an inductive circuit that has current flowing in it.

Yrs,
d