[s-cars] Future PSO/POS and coil replacement alternatives?

[Varon H. Fugman]

Having had two recent POS failures, I've been giving this topic some
thought... and I still have more questions than answers, but I'll toss out a
few ideas...

Heat is enemy of electronics, and the location of the POS modules on the
firewall where they get blasted with radiant heat from the turbo can't be
good.  I've considered relocating them to a cooler location, but where?
Maybe in between the double firewall?  Or maybe an airbox setup like on
various newer Audi models... however, the S4/S6 airbox doesn't seem to have
a suitable mouting surface with sufficent clearence.

That said, it sounds like the '97 to '99 or '00 1.8T A4's are also having
quite a few POS failures, and theirs are mounted on the airbox.  Their
modules look similar to ours, but have 4 channels in a single module with a
4-pin and 5-pin connector.  It is mounted in the top of the air cleaner box
with a heatsink on the bottom side inside the box.  This location would seem
to offer good cooling; the only time they would get hot would be during
post-shutdown heat soak.  Nonetheless, they are still failing (and with only
a single module, the A4 guys can't use our trick of swapping modules to
pinpoint the problem!)

Aren't the newer (~'01 and newer) 1.8T engines (the ones with the POS built
in to the coil) still having a high failure rate of coil packs?  Or has this
been resolved?  Are we sure it was a manufacturing defect, or could it be a
poor design?  I know with the POS failure rate I've experianced, I'm glad
they are *not* integrated with the coil pack on my car!  Is the 225hp
version of the 1.8T exempt from this malady?

Another question:  There is a 3 channel module with the same part number as
ours but without the 'A' suffix on the end.  Anybody know the difference?
For non-turbo V6 cars?

For a device that has to switch primary current to the coil thousands of
times a minute, the POS modules seem a little under-engineered.  I think for
me the ideal alternative would be to build a POS replacement out of
discreate components, with a nice big power transistor with a decent heat
sink.  Not sure yet if this is feasible or how hard it would be... need to
dig out my old college electronics textbook!

What I really cringe at is all the non-lister S-car owners that are having
to pay the dealer $$$ to replace a POS, and the dealer then discards a
perfectly good (to my way of thinking) 2-channel POS!

Varon
'95 urS6

P.S. When it comes to driving the car on 4 cylinders (due to bad POS or
otherwise), my preference is to disconnect the injector for the bad
cylinder.  This will throw a code (open/shorted injector), but keeps a lot
of raw fuel from being squirted into the cylinder, cat, and environment.
And no rotten egg smell.