New to tuning and my truck wont enter closed loop. '04 LS6/4l60 with '98pcm and harness (long story). The truck is running ok but don't think it is entering closed loop. I have a "longtube" header as I have made them and the front sensors are approx. 4ft from the heads. Wonder if o2's are not getting hot enough to enter closed loop. What should I check. I know the ect is working correctly and the closed loop temp. is set low enough to achieve. Any help is good help.