"Most likely what happens is the insulation breaks down and during the
high voltage spike some of that energy shorts out and you get a weak
spark."

Before I go searching in my Bentley, do you know what the resistance specs
should be for the primary and secondary windings in an '89 ?  Is this the
best way to check a coil?

Pat

From:   Dennis Haynes <d23haynes57@HOTMAIL.COM>
To:     vanagon@GERRY.VANAGON.COM
Date:   11/19/2015 07:53 AM
Subject:        Re: crank, wont start
Sent by:        Vanagon Mailing List <vanagon@gerry.vanagon.com>

Most likely what happens is the insulation breaks down and during the high
voltage spike some of that energy shorts out and you get a weak spark. It
may not be obvious when checking but keep in mind the other losses between
the coil and the spark plug, especially the gap between the distributor
rotor and cap pin. A bad coil can even test good with an ohm meter. For
diagnostics it is best to short the output to ground. Besides safety the
open circuit will cause high voltage stress on the insulation. The output
current is really self-limited by the resistance of the output coil. And
yes coils can be damaged by being energized continuously.

Dennis

From: Larry Alofs [mailto:lalofs@gmail.com]
Sent: Thursday, November 19, 2015 10:31 AM
To: Dennis Haynes <d23haynes57@hotmail.com>
Cc: vanagonlist a <vanagon@gerry.vanagon.com>
Subject: Re: crank, wont start

What do you think can cause coil failure, besides simple deterioration
from age and heat?

  Is it a bad thing to short the HV coil wire to ground while doing a
compression test?

Would continuous current thru the primary side cause overheating and
damage?

When I find old coils lying around in vans that I have bought for parts, I
get the feeling that people have changed them attempting to fix other
problems.

Larry A.

On Wed, Nov 18, 2015 at 11:34 PM, Dennis Haynes <d23haynes57@hotmail.com <
mailto:d23haynes57@hotmail.com> > wrote:

Until recently I have not seen the coils fail often. I doubt I have done a
dozen and I know of 5 in the past two years. I keep one on the shelf now.
They are just getting old. I always give thought though to what may have
caused it to fail.

Dennis

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