I just got my LT1 running and it fuel smokes badly. The scanner readings are Left bank 128 and the Right is 151. PCMforless told me that it has an exhaust leak causing the O2 sensor to send a lean condition to the computer. The computer then compensates and richens the mixture. I thought it was a bad sensor so I changed it out. Still the same readings. Even with them unplugged it still reads the same. How does the readings change with the sensors unplugged? I can't find a leak ahead of the O2 sensor but found a small one directly after it at the collector. What gives?
this might be a case of the famous split BLM problem. I corrected it on my brother's car by slowly adjusting the base idle screw on the throttle body and watching the BLMs untill they were equal. The split BLM is caused by valve overlap on larger cams due to the short runner intake design.