Alternator going bad?

G

Gremlinsteve

Greasemonkey
Mar 6, 2018
236
221
43
#1
Reason I'm asking is I just replaced my alternator
It started showing a discharge most of the time on the factory gauge

So I replaced it and I'm showing a discharge still
At idle it's dropping down to 8-9 volts indicated
And at 2500 rpm cruise it shows a 12-12.5 area tops

Measured at battery terminals at idle I'm seeing 12.22 volts

Is the new alternator bad also?
 
Streetbu

Streetbu

G-Body Guru
Supporting Member
May 22, 2011
668
1,102
93
Central NY
#2
Sounds like it. You should see 14.3v all the time...
 
melloelky

melloelky

G-Body Guru
Oct 22, 2017
723
985
93
mass
#3
With the engine running carefully take a screwdriver and place it on the back of the case.if the driver is strongly drawn towards the back it's charging.
 
Z

Zspoiler

Apprentice
Jun 3, 2018
85
54
18
#4
Take it back f you are not satisfied with it.They can bench test them at the store.And if you still have issues,Then you know its not your altrenator.
 
565bbchevy

565bbchevy

Geezer
Aug 8, 2011
5,592
4,494
113
Michigan
#5
I would do all of your testing with a volt meter and test from the output terminal off the back of the alternator and disregard anything your factory gauge tells you
 
airboatgreg

airboatgreg

Royal Smart Person
Oct 2, 2016
1,173
1,105
113
#6
What kind of car?
Alternator type?
gauges or idiot light
 
G

Gremlinsteve

Greasemonkey
Mar 6, 2018
236
221
43
#7
Off the alternator I'm getting 12.2 volts
Not the 14-15 I would expect
 
G

Gremlinsteve

Greasemonkey
Mar 6, 2018
236
221
43
#8
12si alternator
Gauge
El camino 1987 model
 
airboatgreg

airboatgreg

Royal Smart Person
Oct 2, 2016
1,173
1,105
113
#9
make sure you have 12volts to rear of alternator and to red wire that plugs into regulator. Brown wire is turn on so unplug 2 wire connector, start propulsion plant and see if you have 12 volts. With engine running see what your voltage is at the rear output, if it happens to be real high you have an open wire. Rare but something to think about.
If all good bad alternator.
 
G

Gremlinsteve

Greasemonkey
Mar 6, 2018
236
221
43
#10
Ok
 

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