In article >,
Lawrence Glickman > wrote:

> On Fri, 05 May 2006 15:31:12 GMT, "Ed"
> > wrote:
>
> >I'm now thinking there may be a more pervasive electrical problem
> >causing the Herky Jerky symptoms (chuggle).
> >The system voltage always shows up kind of ragged in the scans. Take a
> >look at this:
> >
> >http://www.efsowell.us/ed/ParkAve/Fr...2006_04P18.jpg
> >
> >Here are my notes on the episode shown the
> >+++++++++++++++
> >4.18: 12.4 minutes into trip. CC set at 66 mph, maintaining 67, TCC
> >on. Then
> >speed (or at least the speed sensor?) suddenly drops to 61. Throttle
> >opens (as it should
> >this time!) but seems happy to hold 61 mph for 8-9 seconds, why? TCC
> >stays on. Battery voltage looks rough throughout, between 13.4-13.6.
> >There were a few dives in inj. pulse width before and after the speed
> >fall
> >off.
> >
> >suspicions: Since events seem to be preceded by drop in road speed,
> >could
> >it be a sudden increase in drive-train resistance? Or, ref voltage
> >effects
> >on speed sensor?
> >-----------------
> >
> >Does anyone know if this kind of fluctuation is normal on one of
> >these GM CS-130 alternators?
> >
> >Ed
>
> I looked at the URL graph for battery voltage, and this kind of
> fluctuation is very NORMAL. The voltage regulator isn't designed to
> output a signal more stable that what you see on the graph.
>
> In fact, that's about as good as it gets, on a SCANNER. +Real+
> voltage needs to be monitored at the battery with a DVM. It will be
> higher...from about 13.8 to 14.2
>
> Lg

Ed should also measure the AC ripple at the alternator.
Volt meter set to AC volts, red lead on the alternator output
stud, black lead on battery negative.
Anything over 100mv AC indicates a problem.