electrical charging problem solved - Who done it?

[Eric_R_Kissell at email.whirlpool.com]

The patient was our 1989 200q Avant. The symptoms were a intermittent
battery drain and a resulting voltage degradation per the dash volt
meter.

We encountered this problem during our Easter trip up to my parents. We
were driving on the interstate in heavy rain with radio, wipers,
headlights, and air conditioning operating. About 30 miles into our 180
mile drive, I noticed the volt meter on the dash was near 12V, not at the
usual ~14V. Over the next 40 miles I watched the volt meter continue
dropping. We turned off the radio, wipers and headlights. The AC remained
in use because my wife was 8 months pregnant and she tended to run a
little warm. Because of the heavy rain, driving with the windows down was
not an option. I reasoned that the AC compressor should not hinder the
performance of the alternator because it is driven from the crankshaft
with its own pulley. Nonetheless, the voltage continued to drop so we took
the next exit and happened upon an Autozone.

First I had Autozone check the battery. After a recharge it appeared fine.

Then I had Autozone check the alternator output in the car. Voltage looked
fine but the current capability was very low. In the car the alternator
checked out OK as far as diodes and the regulator, so they hypothesized
that the internals of the alternator must have crapped out. They did not
have a replacement alternator in stock and I did not have any other means
of transportation, so pulling the alternator out of my car did not make
much sense at this point in time. I decided to try to drive onward to my
parents house riding the freshly charged battery. The rain had stopped, so
if we could make the trip before dark we had a shot.

The volt meter on the dash slowly dropped for the next 80 miles, finally
getting down to the point where the idiot light and buzzer started making a
fuss. I was not sure how low the voltage could go before the computer would
shut down, so we took the next exit and happened upon another Autozone. I
took the battery into Autozone and had them recharge it. It was now dark but
we were only about 25 miles from my parents, so I decided to leave the car
and come back the next morning to pull the alternator. I called my brother
who came and retrieved us.

The next morning I pulled the alternator and took it into Autozone. Their
bench test said there was nothing wrong with the alternator. They
recommended that I go to an "auto electric expert" down the street. So, I
went back outside and reinstalled the alternator.  We fired up the car. The
volt meter read ~14V. We went down the street to the "auto electric expert"
anyway, pessimistically hoping they might shed some light on the situation.
I was troubled because I had no idea why the electrical system was working
again. I could not consider the problem fixed until I understood why it
disappeared.

The auto electric shop was a cross between a biker bar and a salvage yard,
all on 2 city lots. The proprietor and other biker-looking individuals
loitering around were all very nice and helpful. One guy on crutches even
told us the story about how he was hit by the same car three times one
recent Sunday on his way to his brother's house to get a 6 pack of beer. I
guess the first two collisions were not persuasive, but the third one broke
bones and resulted in squirting blood so the biker decided not to get back
on his bike and chase the car a fourth time. Anyway, they helped me check
out my car but we ended up at the same conclusion with which we had arrived
- there appeared to be nothing wrong with the alternator or battery or the
connection between them. I figured the best thing to do was to continue
driving the car until the problem returned. That was March 29th.

Fast forward to yesterday, April 15th. My wife calls me at work with a
"its doing that voltage thing again" message. Slap my forehead - I had it
figured out before I left work. I rushed home after work, changed into one
of my shadetree mechanic outfits, grabbed my tools and headed to the best
u-pull-it in town. I knew that my only shot at getting the part I needed
was the u-pull-it, because the local parts stores are hit and miss for my
needs at best. I live in an Audi-sparse town. Even the u-pull-it was not a
sure thing. I also knew that I was tempting fate if I did not get the part
changed ASAP. Luck was on my side as I found a suitable part. I headed
home and installed the part. The problem was solved.

Now for a game: What part did I replace?

Eric R. Kissell
1986 5000cstq, 1.4 bar, K24, Bilsteins
1989 200q Avant, 1.8 bar (SJM), K24, Fuchs
1987 VW GTI 16V, 1984cc, Bilsteins
Evansville, Indiana, USA