Date:         Thu, 20 Jul 2000 23:23:53 -0400
Reply-To:     John <johnpatt@warwick.net>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John <johnpatt@warwick.net>
Organization: PattonSystems International
Subject:      Hand-held tach use with Digifant
Content-Type: text/plain; charset=us-ascii

QUESTION FOR THE LIST:

When working with 2.1L Digifant systems, what do you use to check engine
speed at the engine compartment? (running to the front of the van to
look at the tach doesn't qualify as an answer).

The Digifant system has a unique primary ignition circuit control
perhaps similar to the old capacitive discharge systems. While powerful
and efficient for ignition performance, the Digifant system dynamics are
such that conventional hand-held tachometers cannot read the RPM
correctly. This limitation for hand-held tachs to read the Vanagon
ignition RPM goes all the way back to the air cooled AFC Vanagons.

There is a way to "buffer" the signal dynamics to allow a hand-held tach
to read to the signal correctly. However this procedure only applies to
AFC/California Vanagons. The simple modification is shown in the Bentley
on page 24.11 using parallel resistors at the signal input.

However this modification (for AFC systems) does not provide accurate
RPM readings on Digifant systems presumbably because the resistor values
must be changed to suit the dynamics of the Digifant ignition control.

My question is has anyone determined how to adapt a hand-held tach to a
Digifant system using this resistor-type modification shown on Bentley
page 24.11? If not what are you using to read RPM at the engine
compartment?

Regards,    John