I've been working at getting my Formula back on the road. After replacing the injecters with Bosch III's and tuning with Autoprom the bird has been running much better and BLM were close to 128. But I failed the NJ smog test with high HC's. So I added a bung for the O2 sensor on the passenger side. I got a second O2 sensor for the passenger side and connected this one to the ECU. Upon restarting the ecu leaned out the fuel and dropped the BLMs to 110 or so. I had a voltmeter on the driver side O2 and it was reading 50 to 150 mV. I switched O2 sensors and even swap injectors and the results are the same. It seems like there is extra oxygen on the driver side. My first thought was a vacuum leak on the driver side. I used propane to try and find a leak, but I didn't notice any difference in idle or O2 sensor reading. I also disconnected each injector wire, but that didn't make a difference. It hardly affected idle. Following, I disconnected the plug wires on the drivers side one at a time. It caused the O2 voltage on that side to go up to 300 to 400 mV. Not sure what to make of that; I expected the voltage to go down due to the extra oxygen from the misfiring cylinder.
At WOT both O2 sensors are reading 800-900 mV. So it seems to me that it is vacuum leak, but I can't find it. Its not at the fuel injector bosses or the intake manifold gasket. I have performed the LT1 intake conversion. The EGR is blocked off and disabled. The rest of the mods are in my sig.
Any suggestions would be appreciated.

 

I decided to take the header off and check for leaks. There was evidence of leakage between the header and gasket on the top of the two center tubes. I checked there many times for leaks, but I never felt anything. I also found a leak in the center of the collector. I filled it with water and once it got to the collector it started leaking. Hopefully these two problems are what is causeing the o2 sensor to give a lean reading.

 

I got everything back together and the readings are still the same. Maybe the O2 sensor voltage on the driver side has increased slightly, but it is usually less than 250mV.
Now I think that there might be another problem. At WOT the O2 sensor goes to 0mV. That doesn't make any sense. I guess if there was a miss fire that would happen, but it doesn't seem like its missing at all. I'm not sure what to do next.