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

Raynaud · Accepted Answer

@#@

That GM alternator should run at 14.-14.2v depending on system demand, the volt regulator tries to keep it in the above range. Bad batteries shorts and opens loose connections burnt rectifier bridge bad windings could all create problems.

Ray

Ed · Answer

Thanks, Ray. So, given that this one is bouncing around between 13.4 and 13.6V would you replace it? After checking all the obvious connections, of course.

Have you observed scans like this for a good alternator? Do they always show the fluctuations?

Ed

Raynaud · Answer

@#@ You will see slight fluctuations due to rectification by the diodes , if one or two are open or shorted you will see an sign wave type  scan because it is part alternating  voltage.Ray

Abnormal alternator output fluctuations?

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