Electrical gremlins again

Peter Golledge petergolledge at gmail.com
Tue Jun 1 21:57:41 PDT 2010


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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