I'm tuning a 93 LT1 for a friend. It is a 383 LT4 engine with a 244/244 cam and 30lbs injectors. This thing has been a total nightmare so far. It has long tube headers, and I added a pair of heated O2 sensors. However, the O2's are stuck in the 450 mv range, and barely move, jumping 10 mv or less whether the car is idling or revving. I traced the signal wires back to the computer, and I have continuity with both. Also, the right bank has started slowly dropping in mv, from 450 mv all the way down to 4 mv, while the car is running. It has a 58mm Edelbrock throttle body, and I have drilled two 3/16" holes in it to get it to idle better. The throttle is still open enough to have the TPS voltage at 1 volt at idle, instead of the normal 0.6 volts (is that correct?).
Any help on figuring out why the O2 sensors don't seem to read properly would be appreciated. It sounds like a vacuum leak to me, but it just started after I put the O2 sensors in. Also, it had both SES codes for left and right bank O2's, but after I cleared them they havent come back. Then again, I havent driven the car around yet.

 

Sounds to me like the heater circuits are not connected correctly. You traced the signal wires (I'm assuming you mean the single signal wire from each sensor) back to the PCM, but did you verify that you are getting +12V on one heater wire and a good ground on the other? Typically, the O2 sensors will be at 450mV at cold start, since that is the bias voltage the PCM is supplying. As they warm up, they will start to generate their own voltage, based on O2 level, and the reading will drop to 00XmV's, and the PCM will kick into closed loop and they will start cycling. With the voltage not moving at all on one sensor, I would assume either there is no heat to the sensor, or the sensor is faulty. You can swap the sensors side to side and see if the results (one locked at 450mV, the other dropping to 004mV follows the sensor - sensor problem; or stays wher it was - wiring problem).