[RICK LAKE]

olddog The O2 sensor housing needs a ground and also a large change in the millivolts without and varying will cause the SES light to come on. If you pulled the sensor out of the bung or allowed fresh air to make contact with it and there is no varying of high to low, The light comes on. Most sensor are narrow band and have a .448 MV for the middle of the rich, lean cycle. Untill the sensor reaches 600F most ECU don't use these readings to adjust the fuel and timing when cold or in open loop. This is why most cars and trucks now have heated O2 sensors to get the into closed loop and have the A/F mixture running cleaner and reduce emmissions. The only trick for an o2 sensor in the side pipe is to get it about 6-12" passed the collector so it gets all the cylinders exhaust mixed and not just one. The problem is no room. This is where EGT can come into play and help with tuning. NEVER unplug,remove, adjust a sensor on the car with the power on or running to the ECU, You can spike, loose step count, degree angle, or even blow a quad driver from unhooking a sensor or injector with power on or motor running. No welding without unhooking the battery and ECU also. Rick L. Ps narrow band sensors are about 11.8 to 15.5 A/F readings. The wide range are lower and about under 10 to 18 A/F readings. These are more for racing and power adders. They also cost about 3 times more.