Date:         Mon, 8 Sep 2008 09:54:16 -0400
Reply-To:     Tony Collins <tonycollin@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Tony Collins <tonycollin@GMAIL.COM>
Subject:      Re: Jumpy Tach
In-Reply-To:  <200809071828.AA492765414@intrex.net>
Content-Type: text/plain; charset=ISO-8859-1

Hello Bill,

Is there any loss of power while the tach is going crazy?

Tony

On Sun, Sep 7, 2008 at 6:28 PM, Bill Collins <wb6otg@intrex.net> wrote:

> I'm helping a friend fix up an '87 and we've encountered a problem with the
> tach: at times it will work normally and other times it will read around
> 3000 RPM when the engine is at idle.  Reving the engine a bit and then
> letting off the throttle will cause it to shoot up to between 3 and 4
> thousand RPM, then drop back.
>
> The dash wiring is a mess, but I think we now have all the grounds
> connected.  We have verified that the power and ground connections to the
> instrument cluster are Ok, and cleaned the connector that connects the
> instrument cluster to the wiring harness.
>
> We haven't yet looked at the signal from the coil with an oscilloscope.  I
> did notice I get a shock if I touch the signal lead from the coil, which
> could just be normal inductive kick from the coil, but I would expect there
> to be a diode clamp in the ECU.  Anyone know if this is normal?
>
> Any ideas?
>
> Bill
>



--
82 Scirocco
85 Vanagon