Electrical gremlins again

[Cody Forbes]

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
>
>
> --- On Tue, 5/25/10, Radek <radek at istar.ca> wrote:
>
>
>  From: Radek <radek at istar.ca>
>  Subject: Electrical gremlins again
>  To: quattro at audifans.com
>  Date: Tuesday, May 25, 2010, 5:47 PM
>
>
>  Hi Guys;
>
>  My son's 1988 90Q is acting up again.  I took it to work this  
> morning,
> stopped at a gas station, filled up, tried to start it. It would  
> crank but
> not catch.  I turned the key back, then to "on" again and all  
> instrument
> lights started flickering, then died completely.  I turned the key  
> back
> again, then back to "on" and everything was back to normal.  Tried  
> to start
> it but the starter would just click once and not turn.  Another try -
> everything dead.  This went on a few times so I figured out a busted
> ignition switch.  Got the car push started when the switch was kind  
> enough
> to provide a good connection and eventually got the car home -  
> voltmeter
> would show a bit low, 13V while underway.
>
>  Back at home I changed the ignition switch to a brand new one (had  
> a spare
> one he shelf).  The old switch had the typical broken plastic  
> collar, so I
> thought I was OK.  NO, NO.  The flickering was gone, but starter  
> would not
> crank.  When turning the key to "start", voltage at the battery  
> would drop
> to 6V.  OK, in addition to a broken ignition switch the car may have  
> had a
> shorted battery.
>
>  I put in a new battery (had a spare one on the shelf), fully  
> charged, and
> tried again.  Key turned to "on" - everything seemed fine.  To  
> "start" -
> cranking, and finally the engine runs.  I look at the voltmeter and  
> THE
> ALTERNATOR IS NOT CHARGING.!  WTF?  It was charging before, with the  
> shorted
> battery and a broken ignition switch!  Voltage at battery with engine
> running was showing 12V.
>
>  I put in a spare voltage regulator (had a spare one on the shelf)  
> and it
> still isn't charging!
>
>  Where to look next?
>
>  Radek, Ottawa
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