Originally Posted by Nixlimited

Getting an A/F reading based on the OEM sensors is not going to give you all the information you want. In most cars, the OEM O2 sensors are narrowband and are only meant to be accurate in a range around 14.7 since that's what the car will target in cruise mode (i.e. not under load). If you want to measure A/F accurately on an FI car, you need a standalone wideband sensor.