Chevy low alternator voltage output cold

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tss212 - 17 Dec 2007 05:11 GMT

I have a 1989 C1500 with a 350. The voltage will be erratic when motor
goes above 1500 rpm when cold. After it warms up the voltage will
become steady around 13.8 volts. At first startup it goes a little
over 14 volts until the motor speeds up. When it idles back down the
voltage rises back up. What could be the problem. I replace the wiring
to the regulator plug and the output wire. Please help

Tim Slover

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Tim - 18 Dec 2007 09:52 GMT

> I have a 1989 C1500 with a 350. The voltage will be erratic when motor
> goes above 1500 rpm when cold. After it warms up the voltage will
[quoted text clipped - 4 lines]
>
> Tim Slover

Ok Tim Here we go!!!
It sounds as though without seeing the truck that the brushes are
getting stuck. is there a lot of belt dust or oil on or around the
alternator? If you have a low charge when cold,, it's a sign that your
belt is slipping. Check that belt first. If there is oil on the
Alternator, Replace that alternator and get rid of that oil leak.
on the plug that goes into the alternator,, put some silicon sealer
around the plug after you put the plug in. we have found that plug will
vibrate and cause erratic charging problems too
Later
Tim
PASCO, We are your charging and starting specialists
410-546-2041

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Mike Romain - 18 Dec 2007 18:05 GMT

My 86 Jeep CJ7 with it's 'GM' AC Delco alternator just started doing the
same thing again. I need a new fan belt again.

In my case it is always a belt getting shiny. They get polished up from
mud (liquid sandpaper) and dust because I off road lots, then they start
slipping under load when cold, then all the time. Mine just went to all
the time because it is cold out....

I test mine by seeing if I can hand slip the alternator pulley on a cold
off engine. If I can hand slip it, it will slip under load.

I have a V belt which is more prone to this, but a serpentine can also
polish up.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com

> I have a 1989 C1500 with a 350. The voltage will be erratic when motor
> goes above 1500 rpm when cold. After it warms up the voltage will
[quoted text clipped - 4 lines]
>
> Tim Slover

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Scott Dorsey - 19 Dec 2007 14:35 GMT

>I have a 1989 C1500 with a 350. The voltage will be erratic when motor
>goes above 1500 rpm when cold. After it warms up the voltage will
>become steady around 13.8 volts. At first startup it goes a little
>over 14 volts until the motor speeds up. When it idles back down the
>voltage rises back up. What could be the problem. I replace the wiring
>to the regulator plug and the output wire. Please help

Could be anything from bad brushes to cold solder joints in the regulator
which become more solid when they heat up.

It may just be easier to swap the whole thing out.
--scott

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