O2 voltage going to zero


I had to replace my stock 56K turbo on my TTA because it died. I also had to replace the downpipe due to damage from a deer. Now, naturally there were a few other things that I found and fixed or added in the process. Mini-starter because mine clicked a few times back in the summer, IAC angle mount for obvious reasons, 50lb injectors with a new Turbo Tweak chip, E3 spark plugs, dump pipe, etc. I also found a small crack in the passenger header and had that welded.

Anyway, the car is back together and it starts right up and runs perfectly. It actually drives fine and I've driven it to work and back and put nearly 90 miles on it. The problem is the O2 voltage goes to zero when I'm driving. It actually held between 000 and 007 at 65-70MPH for several miles with the cross counts around 95-100. It does appear to cycle at these low levels and it's a brand new AFS-22 O2 sensor. As soon as I stop it will return to normal cycling at idle.

I can detect no exhaust leaks, no vacuum leaks, and no other obvious problems. The BLM is at 142 and the INT is at 160 while driving, but they both come down around 128 at idle. It should be running rich as a pig, but it doesn't smell rich at the tailpipes. It does however blow black smoke on light acceleration. I obviously haven't had the car over 8-10psi because I want to keep it in one piece!

There is a very quick whistle when I bump the throttle really lightly while parked. I can't hear it while driving. It's gone as fast as it starts and it doesn't happen at all if you bump the throttle a little harder. This is why I was checking for a vacuum leak with carb cleaner, but I haven't found anything.

Any suggestions?