plug wire fault detection the hard way

[Doyt W. Echelberger]

Last week my 87 5ktq engine (at 300k miles) started missing on one cylinder
at idle. I figured it had reached the end of its life, at last, and visions
of a 95 S6 danced in my head. But it wasn't Christmas, so I started the
detctive work...... Paper banknote at the tailpipe fluttered like a machine
gun. Thought about a leaking exhaust valve, but 5 cylinder Audi engines
don't have that kind of reputation, even at 300k miles. So, I started
pulling plug wires to see if anything changed, and sure enough, #5 didn't
make any difference.

I removed the plug and it was gapped within specs and not loose or cracked,
and had good color.

I swapped in a used plug wire from my collection, and the miss went away.
Engine never ran so smooth. Must have been causing problems for months. But
the story isn't over. There was a nasty-sounding low-pitched whine in the
background, coming from the front part of the engine compartment. Failing
AC clutch? Bad alternator? I had just replaced the alternator a few weeks
ago, and the whine sounded louder on the alternator side, so I checked the
output voltage and it was about 8 volts.  That rebuilt alternator had
failed. Checked the battery voltage and found about 11 volts......in a
battery about 6 months old. Charged the battery and got back to 13.6 volts.

Alternator was still under warranty, and I got another one free. Put it in,
and saw charging at 14.2 volts.  Problem solved.  Also, learned how to find
bad plug wires, the hard way. All you have to do is drop the low-side coil
voltage until the bad plug wires don't work anymore.

Not sure anyone else should try my new method.

Doyt Echelberger
87 5ktq at 300k miles, in Ohio   USA