Electrical gremlins again (crazy needle syndrome)

[Radek]

Car drives fine and, after cleaning connections at the starter, alternator and battery terminals, starts without issues.  However, the voltmeter needle still fluctuates at idle.

So I measured DC current at alternator (positive probe to lug terminal, negative to the battery) with a digital meter - fluctuates slightly around 14.4V (14.37 - 14.44 or so).  Next, I measured the same with a needle meter - shows steady around 14V.  In other words, hand held meters show ok, voltmeter in the dash fluctuates.

So next, I removed the volt gauge from the dash and connected it directly to the alternator and the negative bettery terminal, to rule out wiring issues.  Started the engine and it really went crazy!  With engine at idle, abour 900 rpm, the needle would jump up and down between 13 and 16 volt.  With engine running above 2000 rpm, it would narrow down, oscillating between 14 and 16 volt.  It would not go below battery voltage, though.

I measured AC current at the alternator. Shows 30 - 31 volt.  Alarm!  However, I measured AC across battery terminals and it shows 28 volt, with battery disconnected from the car. Should AC be showing 0?

I swapped the voltage regulator for another used one - no change.  Is voltage regulator the only device that converts AC to DC, or are there other electronic devices on the alternator that could have failed?

I cleaned battery teminals and all connections I could find.  Small Audis have no splice, battery is in the engine compartment.

Any ideas?  Do I need a new alternator or a new volt gauge?

Radek.

------------------------------

Message: 4
Date: Wed, 2 Jun 2010 05:16:19 -0700 (PDT)
From: Andrew Dickinson <amdickinson at rogers.com>
Subject: Re: Electrical gremlins again
To: quattro at audifans.com
Message-ID: <407006.58056.qm at web88308.mail.re4.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

Also, the 'crazy needle' syndrome would indicate a short or open wire issue to me if when it drops it is below the battery voltage.? For the short you may be able to follow your nose to burnt wire.? For either instance it appears to be intermittent so banging the car in different places may prove fruitful to narrow down location as well.? HTH.


--- On Wed, 6/2/10, Cody Forbes <cody at 5000tq.com> wrote:


From: Cody Forbes <cody at 5000tq.com>
Subject: Re: Electrical gremlins again
To: "Peter Golledge" <petergolledge at gmail.com>
Cc: "Radek" <radek at istar.ca>, "<quattro at audifans.com>" <quattro at audifans.com>
Date: Wednesday, June 2, 2010, 7:44 AM


You also might want to check for AC current with a multimeter. Failed? 
diode(s) can put AC current into the system and give all sorts of? 
funny issues. There will usually be a minimal amount, like less than 1? 
volt, anything more than that is no good.

-Cody (mobile)

On Jun 2, 2010, at 12:57 AM, "Peter Golledge"? 
<petergolledge at gmail.com> wrote:

> Since the battery _should_ act like a capacitor I think you still have
> either intermittent ground or positive battery terminal to see large? 
> voltage
> swings.? Since you don't mention below check/clean the battery? 
> ground cable.
> I had a loose one of the those drive me nuts in a 5000.? Not sure if? 
> the
> smaller audis had the dreaded "splice" in the positive cable at the
> footwell, others would have to comment on that as a possible cause.
>
> As for the source of the surging voltage I'd suspect a voltage? 
> regulator,
> they can be replaced with the alt in place and the they are relatively
> cheap.? You might want to pull the regulator and check the brushes? 
> as well
> as the regulator ground to the alt.
>
> -----Original Message-----
> From: quattro-bounces at audifans.com [mailto:quattro- 
> bounces at audifans.com] On
> Behalf Of Radek
> Sent: Tuesday, June 01, 2010 8:27 PM
> To: quattro at audifans.com
> Subject: Re: Electrical gremlins again
>
> Thanks to all you guys for putting me on the right track.? So far, I
> replaced the ignition switch (old one was broken), and the battery? 
> (old one
> would drop to 8V when the key is turned to run).? I cleaned? 
> terminals at the
> alternator, the starter and the jumper strip in the relay box, and? 
> replaced
> about a foot of wire at the solenoid (old wire had corrossion, white? 
> powder
> was falling out from between the strands of aluminum).? I also added? 
> an
> extra ground between engine block and the chassis with a heavy gauge? 
> wire
> (thickness of your little finger).
> Car started five times in a row, so far.
>
> What worries me, though, is that while there is 13.8 V at the? 
> alternator
> when charging and nearly the same (like 13.78) at the battery, the? 
> voltmeter
> fluctuates.???Car idles at about 900 to 1000 rpm (too high, I know,? 
> I'll get
> to it next).? At 1000 rpm the voltmeter needle is fairly steady,? 
> there is
> just some barely visible vibration. However, when rpms drop, the? 
> needle
> (sometimes, not always) goes crazy, jumps up and down.? Could that? 
> indicate
> a charging problem that could have killed the old battery?
>
> Radek