B5 V6 "unilateral" misfiring

[Chris Newbold]

On Mon, Apr 14, 2008 at 12:52 PM, Huw Powell <audi at humanspeakers.com> wrote:

>  After reading everything you have tried on the spark side (and imagining
> that you have verified all-good electrical connections), it sure sounds like
> a fuel issue.  Are the two sides managed separately?  Could 4-5-6 be running
> too rich?  So rich the system can't get them back to stoich?

I have not yet dug into the wiring; I need to sit down with the
diagrams and figure out what's common to 4-5-6 for both ignition and
fueling.

The data from the O2 sensors suggests that 4-5-6 are running slightly
richer than the ECU expects-- that's the source of the
across-the-board -3.5% leaning-out. This is just within the factory
spec (+/-4%) but well within the control "headroom" so I think that
the ECU could lean things out even further if it wanted to.

The fact that it's leaning out across the entire RPM range might hint
that its fuel and not ignition, though, unless it's just misfiring
constantly. I'm not sure what would cause the mixture to be richer
than expected, though. I suppose wiring trouble could cause any sort
of outcome...

-Chris
2001.5 S4 Avant 6spd