[V8] A8 misfire

[Buchholz, Steven]

> Being an A8 owner and V8 list occasional lurker, I thought I'd try
> posting here about another pals 97, A8, 3.7 ltr. Woes.
> Trouble code is misfire cylinder #2
> We have
> Changed the plug
> Swapped POS's
> Swapped coils
> 
> Does this point in some general problem direction?  We will 
> test wiring
> from ecu to pos and pos to coil.  Then swap injectors and 
> test injector
> wires too.
> Main fear of course is a bad ECU.

... it would be extremely difficult to figure some way that an ECU could
fail and cause a single cylinder to misfire ... so the "main fear" should be
allayed ...

For some reason the TLA "POS" is escaping me ... but I think your debugging
method is the correct one.  Since you've swapped the coil, plug and "POS"
the next thing to do would be to check the intervening wiring.  

Do you know if the cylinder ever fires?  If you touch the #2 exhaust header
when starting a cold engine does it get hot?  Does a new plug show any sign
of combustion in the cylinder?  If the wiring checks out and the cylinder is
firing at least some of the time you may want to check compression on #2.
Oh yes, one more thing ... check the fuel injector for #2.  I'm pretty sure
that the "misfire" condition is actually detected via the OXS (ECUs are much
more sophisticated now than they were even back in 1990) ... what the ECU is
probably detecting is that the exhaust pulses for cylinder #2 are out of
line and that is why the misfire code ... 

HTH!
Steve B.
San Jose, Kaleefohnia (USA)