At 5:20 PM 10/19/98, Al Knoll wrote:
>Piqued my interest.  Just what information does the VW stock 89 cruise control
>get and where does it get it.  Motor speed via tachometer?  Driveshaft
>rotation?
>How does it know how "fast" the venerable beast is going?  I recently had a
>miserable experience with an alarm installer who botched a bunch of things on
>the van.  Tach no longer works, speedo cable ripped off the speedo, broken tab
>on the instrument cluster housing so the cover rattles etc etc.
>
>And of course the autopilot doesn't work now.  So what should I check to see
>what other damage they've done re the cruise control.  It would help if I knew
>what signals the CC uses and from where they originate.
>

        The system uses vacuum from a vacuum pump (not manifold vacuum)
        to power the vacuum servo that adjust throttle to maintain the
        speed setting. With the exception of a vacuum connection to
        brake and clutch (if so equipped) vent valves, the rest of the system
        is electronic. The brake and clutch vacuum sensors are also backed up
        by electronic ones as well as sensors connected to the brake light
        circuit for safety and redumdancy. Speed sensing is done by an
        inductive pickup on the speedometer (where cable enters speedo in back
        of instrument cluster). Controller (remembers state of settings and
        hard lowspeed cutoff limit, and monitors sensor states cutting cruise
        off if sensor failure detected) is located behind the instrument panel
        on the right side...

        Get a Bentley and you'll find all the info you need for testing
        and analysis of the CC.

      OLTECO                    Ari Ollikainen
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