Ignition troubleshooting - how not to.

[Peter Golledge]

Listers,

Some things can make me wish for another heater core replacement on the
Audi.

My 79 930 Porsche has had an intermittent fault ever since I have owned
it.
It will die without warning and will not restart for a few minutes...
sometimes there
would be months between events.

Initial suspects like fuel pumps (yep 2 pumps, more points of failure
y'know) were
ruled out.  All of the ignition tests checked out fine in the garage hot
or cold.
Checking for spark on a flat six and a distributor lodged firmly under
the intercooler
is not fun to say the least.  OK we have a no spark condition but it
goes away...

Coil input ohms are less than spec, change it out just in case.

Check out the CDI unit, hmmm the original is there and so is a nice
Permatune unit which
is not restrained and rattling nicely.  The permatune is hooked up,
can't contact PO to
find out why but I suspect this was dropped in during troubleshooting.
After removing
the 23 year old Bosch unit and mounting permatune properly things go
well for a while.
The Bosch OE CDI is $1K+ new, I figure I'll keep the old unit "just in
case".

The gremlin lies in wait for a P-club track event and strikes, complete
no start.  OK
tow to home, should be easy to fix now.... fires right up at home. :-(

Today I rig up test wires running from the CDI input/output and power
into the cabin
so I can check things out.  Outbound run is without a hitch,  heading
back it is
threatening snow (Denver CO) once the snow starts the car stops.
Changing a Porsche
CDI crammed into a little space next to a hot motor in snowstorm, oh the
joy of classic
motoring.  The 23 year old CDI works just fine.... now all I need to do
is navigate
rush hour in a 930 running summer tires.

Cheers
--
Peter Golledge