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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


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