Smokin'

[MustangGT]

#5 and #6

[MustangGT]

#7 and #8

[Barry_R]

She sure looks fat... (be very careful how you say that around the house if you're married...)

I might want to look at leaning out that part of the map to clean things up.  The O2 data is not going to be accurate with that kind of action going on - the sensor might look like the plugs.

Other possibility is getting into valve float.  Not likely, but that seems like a pretty sharp drop off.  Its been a long time since I saw that one now - but how does your recent dyno chart look?  We might be able to compare curve shapes rather than numbers.  It should show a soft roll off from power peak - a hard, sharp drop can indicate a loss of valvetrain control.  If its questionable we might want to pull a rocker arm set and look at the valve top wear pattern.

[cjshaker]

Plugs are definitely showing very rich. And like Barry said, if the O2 sensors are sooted that bad, it could be skewing the readouts.

I take it this is a fuel injected engine? I have zero experience with that, so I can't help, but to me that nosing over at the top end is too harsh to be caused by fuel. Rather, I think the black smoke may be, at least in part, a result of the engine doing something it shouldn't be doing. It sounds like loss of valvetrain control to me, but the dyno graph should really help in showing if that is the case.