There isn'ty such a thing as a pre-cat O2 sensor.

You have upstream (used for fuel trim control) and downstream (used for catalyst monitor) O2 sensors.

The MIL-eliminators (or non-foulers) can only be applied the the downstream sensors. The upstream ones are mandatory for proper engine operation.

Steve

98 Contour SE Sport 2.5 Duratec ATX The wifey's car 89 Taurus SHO - 246K miles 94 SHO ATX - 190K 1997 F-150 5.4L ATX - The Workhorse 150K. ANY THREAD WITH "OMG" or "WTF" ETC IN THE TITLE WILL BE IGNORED!