Alternator light stays on

Hello.

I'm still not totally confident in my skills as a mechanic, so I'd like
to run something by you all just to confirm that I'm either on the right
track or completely wrong.

My car is a 92 Jetta, 1.8 gas w/AC. Around 230,000 km, and still
treating me right...most of the time.

Today, out of the blue, my alternator light stays on while the engine is
running. It actually seems to "flutter" really fast, rather than just
stay full on. I ran through some tests:

-Battery is fine. It's fairly new, still shows 12V with engine off.
-Alternator belt is good. I replaced it last year, it's still tight, and
the alternator spins merrily when engine is on.
-Cleaned and reseated battery connections. Wires are okay.
-With engine off, negative cable disconnected, I can put a test light
between negative post on battery and negative cable and get nothing, so
there isn't a short anywhere.
-With engine on, I read ~11.7V across the battery at idle and at a couple
thousand rpm. With electrical accessories on, voltage is near the same,
~11.5V.

According to Bentley, that last point indicates the problem PROBABLY lies
in the regulator. To be clear, Bentley says that if you check voltage
across the battery with accessories off and compare that with accessories
ON, and the result is about the same, it's probably the regulater,
whereas if the voltage is LOWER with all the accessories on, it's
probably the alternator. Question is, what exactly does Bentley mean by
"lower"? How much of a difference would I be seeing? My headlights are
on all the time, and my stereo was recently stolen, so really the only
accessories I can turn on and off are my blower fan and rear-window
defrost.

I've read other info that says 90% of "alternator" issues are fixed by
replacing the regulator. I do hope it IS the regulator, because I can't
afford another alternator right now. Is it fairly safe for me to point
the finger at the regulator and install a new one as my first step? It
looks pretty simple...any pitfalls waiting for me?

Thanks in advance!

Lamprey wrote:

> -With engine on, I read ~11.7V across the battery at idle and at a couple
> thousand rpm. With electrical accessories on, voltage is near the same,
> ~11.5V.

The nominal voltage is 14.0 Volts, if you read more than 14.5 at any
RPM, the regulator is the primary suspect. Reading voltages below 14V,
as you do, certainly *can* be a broken regulator (although in my
experience, regulator failures usually result in over-voltage, not
under-voltage) but it is just as likely to be worn-out brushes. If the
alternator is original to the car and has never been serviced, I would
start out with a new set of brushes. They should be even cheaper than a
new regulator.

Randolph wrote:

> Lamprey wrote:
>
>
>>-With engine on, I read ~11.7V across the battery at idle and at a couple
>>thousand rpm. With electrical accessories on, voltage is near the same,
>>~11.5V.
>
>
> The nominal voltage is 14.0 Volts, if you read more than 14.5 at any
> RPM, the regulator is the primary suspect. Reading voltages below 14V,
> as you do, certainly *can* be a broken regulator (although in my
> experience, regulator failures usually result in over-voltage, not
> under-voltage) but it is just as likely to be worn-out brushes. If the
> alternator is original to the car and has never been serviced, I would
> start out with a new set of brushes. They should be even cheaper than a
> new regulator.

I agree, but I've never seen a factory VW regulator put out much *over*
14V - they seem to run at a lower voltage than American stuff by their
nature.

nate

--
replace "fly" with "com" to reply.
http://home.comcast.net/~njnagel

Maybe as easy as the voltage regualtor, but if the slip rinds are worn then
it's a good idea to get a rebuilt alt.

"Lamprey" > wrote in message
news:trVTd.510742$Xk.475248@pd7tw3no...
> Hello.
>
> I'm still not totally confident in my skills as a mechanic, so I'd like
> to run something by you all just to confirm that I'm either on the right
> track or completely wrong.
>
> My car is a 92 Jetta, 1.8 gas w/AC. Around 230,000 km, and still
> treating me right...most of the time.
>
> Today, out of the blue, my alternator light stays on while the engine is
> running. It actually seems to "flutter" really fast, rather than just
> stay full on. I ran through some tests:
>
> -Battery is fine. It's fairly new, still shows 12V with engine off.
> -Alternator belt is good. I replaced it last year, it's still tight, and
> the alternator spins merrily when engine is on.
> -Cleaned and reseated battery connections. Wires are okay.
> -With engine off, negative cable disconnected, I can put a test light
> between negative post on battery and negative cable and get nothing, so
> there isn't a short anywhere.
> -With engine on, I read ~11.7V across the battery at idle and at a couple
> thousand rpm. With electrical accessories on, voltage is near the same,
> ~11.5V.
>
> According to Bentley, that last point indicates the problem PROBABLY lies
> in the regulator. To be clear, Bentley says that if you check voltage
> across the battery with accessories off and compare that with accessories
> ON, and the result is about the same, it's probably the regulater,
> whereas if the voltage is LOWER with all the accessories on, it's
> probably the alternator. Question is, what exactly does Bentley mean by
> "lower"? How much of a difference would I be seeing? My headlights are
> on all the time, and my stereo was recently stolen, so really the only
> accessories I can turn on and off are my blower fan and rear-window
> defrost.
>
> I've read other info that says 90% of "alternator" issues are fixed by
> replacing the regulator. I do hope it IS the regulator, because I can't
> afford another alternator right now. Is it fairly safe for me to point
> the finger at the regulator and install a new one as my first step? It
> looks pretty simple...any pitfalls waiting for me?
>
> Thanks in advance!

Forgive my ignorance...what are slip rinds? Same as bearings?


"Woodchuck" > wrote in
:

> Maybe as easy as the voltage regualtor, but if the slip rinds are worn
> then it's a good idea to get a rebuilt alt.
>

Never mind...I just woke up. Slip rings, yes? How would I tell if they
were worn?


Lamprey > wrote in news:zK1Ud.514809
$6l.263901@pd7tw2no:

> Forgive my ignorance...what are slip rinds? Same as bearings?
>
>
> "Woodchuck" > wrote in
> :
>
>> Maybe as easy as the voltage regualtor, but if the slip rinds are worn
>> then it's a good idea to get a rebuilt alt.
>>
>

Just look visibility to see if the regulator brushes wore a grove in them.

"Lamprey" > wrote in message
news:SP1Ud.514821$6l.276086@pd7tw2no...
> Never mind...I just woke up. Slip rings, yes? How would I tell if they
> were worn?
>
>
> Lamprey > wrote in news:zK1Ud.514809
> $6l.263901@pd7tw2no:
>
>> Forgive my ignorance...what are slip rinds? Same as bearings?
>>
>>
>> "Woodchuck" > wrote in
>> :
>>
>>> Maybe as easy as the voltage regualtor, but if the slip rinds are worn
>>> then it's a good idea to get a rebuilt alt.
>>>
>>
>

Nate Nagel wrote:

> I agree, but I've never seen a factory VW regulator put out much *over*
> 14V - they seem to run at a lower voltage than American stuff by their
> nature.

Agreed. The Bentley indicates 14V +/- 0.5V. My experience (two
alternators in my '87 GTi) is that the voltage is within 50mV of the
nominal 14V.

Thanks for all the info, folks. I pulled the regulator/brush assembly out
and the brushes were worn to almost nothing. Flicked the brushes a bit to
loosen the springs, reinstalled (this actually made the alternator light go
out, but I knew it still needed to be replaced) and drove to my FLAPS to
buy a new assembly ($38 CDN w/tax). Problem solved, and for cheaper than I
expected, hooray hooray!

Had a look at the slip rings while I was in there, and they looked
"experienced" but smooth. No visible abnormalities that I could see. So,
hopefully I'll get a bunch more mileage out of that alternator.

Thanks again, everybody!