Get the codes read rather than just shooting in the dark, also the rear O² sensors have nothing to do with engine control and would not affect its operation. They only monitor the catalytic converter efficiency.
You did not say, is the X-pipe an "off road" unit--I.e. no cats? And as lowflyn
asked, you did install the MIL Elininators on the rear sensors only--right?
The rear sensors have to be fully functional for MIL Eliminators to work--more about how they work and how to make your own for $5 or so here
. The O² sensors can be bench tested with a miultimeter and a propane torch--he is how to do that
- 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq