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Old 09-13-2013, 08:26 AM
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Voltage drop at 2000 rpm

I've poked through the forum and haven't found an answer so here's my issue:

05 6.0 crew cab dually 4wd KR w/150k, EGR delete and studs

Coming home Tues eve, battery light went on while on the highway, flickered and went off. I switched my CTS to show batt volts and continued driving. FICM stayed around 48 but batt fluctuated from high 11's to mid-13's. Had the alt tested on the truck and it tested bad so I replaced it. Worked fine for Weds but now is doing the same thing.

Idle to just shy of 2k yields 13.1-13.4V, cross over some magic RPM and it drops to ~12.

This is irrelevant of AC, headlamps, radio, HVAC, etc... I've tried all of them on and off. I've checked wires off the alt and batt grounds and they seem ok.


Any ideas? Anyone???

Thanks in advance,
Chris
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Old 09-13-2013, 10:08 AM
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Only thing I can think of off the top of my head is a belt slipping at that rpm range.
Check your belt tensioner and pulleyes.

Does the a/c do anything different at that rpm range?
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Old 09-14-2013, 08:16 AM
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I was also thinking about belt slipping but the AC works fine at all RPM and it would seem to me the compressor would slip before the alternator. I did check the tension and it seemed like it was tight enough. The belt is about (less than) 2 years old with less than 35k on it.

Might it be the regulator? Did I get a bad "new" alternator?
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Old 09-14-2013, 07:09 PM
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Quote:
Originally Posted by ckouba View Post
Did I get a bad "new" alternator?
Apparently the answer is yes.

I kept thinking about the regulator as the symptoms were very consistent- get to just shy of 2k and the output drops. Slow it down to 1800 or so and it pops back up.

Called my parts guys and chatted with them, and they also thought it sounded like the regulator was bad and warranteed me a new alternator. Conveniently, the new one is even a different brand remanufacturer as well. Swapped it in this morning and things seem normal now. It did this last time too so I'll wait a little before officially declaring victory but initial results look good.

Chris
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