Abnormal alternator output fluctuations?

Question

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:

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Here are my notes on the episode shown there:

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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?

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Does anyone know if this kind of fluctuation is normal on one of these GM CS-130 alternators?

Ed

Lawrence Glickman · Accepted Answer

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

aarcuda69062 · Answer

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.

Knifeblade_03 · Answer

aarcuda, is that reference voltage specific for GM alternator, or doesit apply to other brand alternators [e.g. Ford, Chrysler?]

fiveiron · Answer

if you expect / want a steady read, then you might switch to dc - andforget all the little factors involving ac current.mhov=83e

Ed · Answer

Sorry, I don't follow. If you are referring to the JPG file, it is from a OBD-II scanner.No AC option.Edif you expect / want a steady read, then you might switch to dc - andforget all the little factors involving ac current.mhovfe

aarcuda69062 · Answer

Fits all brands.

aarcuda69062 · Answer

Why would anyone want to skip an important diagnostic step?Do you have the slightest idea how electricity is generated in an alternator?  (left you a clue there)

Abnormal alternator output fluctuations?

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