Date:         Mon, 31 Mar 2003 11:33:15 -0800
Reply-To:     laurasdog@WEIRDSTUFFWEMAKE.COM
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Steve Delanty <laurasdog@WEIRDSTUFFWEMAKE.COM>
Subject:      Re: VDO Tach weirdness
In-Reply-To:  <KBEPLEMPKLMJNLJAGDLJKEDBCCAA.lists@slapnose.com>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 10:58 AM 3/31/2003, you wrote:
>Hi,
>
>Can anyone explain to me why this would happen:
>After installing my new tach, I started the engine. The reading was way too
>high (2-3000 or more). So I went in the back and hooked up my tach/dwell
>meter. When the meter was connected in the back, the readings matched up,
>i.e. the tach on the dash dropped to what seems to be a correct reading.
>With the tach/dwell disconnected, the dash tach jumps up.

It sounds like the tach is picking up some ringing from the ignition
system and counting it as multiple pulses. Putting the dwell/tach
on kills enough of the ringing to make the tach happy.

Goto Radio shack and get a 470 ohm 1/4 watt resistor and a
.01 uF ceramic disc capacitor (rated at least 50 volts)

Put the resistor in series with the wire to the tach, and the
capacitor from the tach side of the resistor to ground.

That simple little R/C network will help kill the noise on the tach
wire.

Steve