Alternator stops charging above 4K. - Chevy Impala SS Forum
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post #1 of 13 (permalink) Old 07-11-2017, 12:16 AM Thread Starter
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Alternator stops charging above 4K.

I recently replaced the alternator in my Caprice--one day it just stopped charging at all. I bought this new Remy 140-amp model with lifetime warranty from Rock Auto: https://www.rockauto.com/en/moreinfo...=1037461&jsn=1

I noticed tonight that when the tach went past 4000 RPM, the lights dimmed and the voltmeter dropped from the low 14s down to the upper 12s. As soon as RPM dropped below 4000, the lights went back to normal, as did the voltmeter. (My '94 Caprice has an F-body gauge cluster.)

This alternator has only been on the car for less than a month, and maybe 600 miles. Is it likely that anything else is amiss, or should I just contact RockAuto for a replacement?

--'94 Caprice "SS" wagon, 0.30 over, high-volume oil pump, LT4 hot cam, 1.6:1 rockers, ported aluminum Corvette heads, shorty headers, PCM4Less tune, 4.10s, shift kit, side-exit dual exhaust with Flowmasters, OR X-pipe, F-body gauge cluster, Bonneville front and rear seats (working electrics), Bravada console shifter, Bilsteins, 12.7:1 Impala steering box, Boss 338s with 255/45R20s, bunch of other stuff I'm forgetting.
--'04 Mustang Cobra, '15 Audi S4
--1125R, 1050, VMax, VFR800, DRZ-400E
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post #2 of 13 (permalink) Old 07-11-2017, 06:13 AM
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Flesh, time to break out the VOM. Start by checking voltage at the alternator and work your way to other points. Battery and such. See if there is a drop anywhere along the line. How are all your grounds? Check your hot connections too. You could also take your alternator to Advance or AZ to see if it's your new alternator. How's your belt tension? Might be slipping at higher RPMs. I'm sure you will get more and maybe better thoughts on this, but right now that is all I can think of.
Good Luck Friend,
Mark: Snowman-33

93 9C1: Work & Cubic Ca$h This started with a new headlight and fender Celeritas In Conficiendo
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post #3 of 13 (permalink) Old 07-11-2017, 07:37 AM
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There could be a loose winding, that disconnects at higher RPM. The alternator runs at about 2 1/2 or more times the engine speed. It could also be the regulator that must switch the voltage as the RPMs increase. The regulator is internal for the alternator. The regulator is included in the warrantee.

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post #4 of 13 (permalink) Old 07-18-2017, 06:35 PM
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Not trying to Jack your thread but thought fred might know.can a alternator drain your battery?i installed a used alternator and now my battery goes dead in a few hrs.
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post #5 of 13 (permalink) Old 07-18-2017, 07:58 PM
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If there are some shorted diodes or in the regulator circuit, it can happen.
How often...??
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post #6 of 13 (permalink) Old 07-18-2017, 08:02 PM
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Everytime.less than 12 hrs its so dead not even dome light.i installed old alternator tonight.going to see if it starts in the morning.
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post #7 of 13 (permalink) Old 07-18-2017, 09:47 PM
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Meant 'how often do diodes short out rather than burn out open circuit' is was my question. But you might have gotten the lucky one.

You can see if the batt terminal shows a short to case when you take it out. or any of the other terminals to case.
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post #8 of 13 (permalink) Old 07-19-2017, 08:20 AM
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Put old alternator back on and let set over night and car started right up
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post #9 of 13 (permalink) Old 07-26-2017, 12:04 AM Thread Starter
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I received and installed the replacement alternator today and the problem is solved. Voltage while engine running is a bit higher on the dash gauge than before, and it remains consistent all the way to 6000rpm.

--'94 Caprice "SS" wagon, 0.30 over, high-volume oil pump, LT4 hot cam, 1.6:1 rockers, ported aluminum Corvette heads, shorty headers, PCM4Less tune, 4.10s, shift kit, side-exit dual exhaust with Flowmasters, OR X-pipe, F-body gauge cluster, Bonneville front and rear seats (working electrics), Bravada console shifter, Bilsteins, 12.7:1 Impala steering box, Boss 338s with 255/45R20s, bunch of other stuff I'm forgetting.
--'04 Mustang Cobra, '15 Audi S4
--1125R, 1050, VMax, VFR800, DRZ-400E
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post #10 of 13 (permalink) Old 07-26-2017, 02:17 PM
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What kind of set up do you have to pull those RPMs? I can say I've never touched those levels.

Fred SSmidt
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