I didn't make it two miles from the shop and the CEL came on. Guess I need to get some O2 simulators? Any other suggestions?
No need for O2 simulators.
1.Just weld one "O2 bung" into each midpipe (if it wasn't done - which would lead me to question the automotive knowledge of the fabricator/installer) and install the lower
O2 sensors. It's the right way to do it.
2. Make sure you use OEM Nissan (all metal stainless) flange gaskets. The cheap non-OEM gaskets leak or blow out from too much WOT exhaust pressure (I made this $15 mistake).
3. Check that the new flanges (of the new de-cat pipes) are perfectly flat with the opposing flanges. Any leak here will throw CEL codes.
4. Seach this forum for resetting the CEL light using series of "timed" steps using the ignition switch and gas pedal.