less power with new oxygen sensor

code indicates position 1 oxygen sensor malfunctioning.After installing new aftermarket sensor the car performs worse with barely enough power to drive prior it had loss power but not as bad.I performed the oxygen sensor replacement.i then reinstalled the old sensor and it gained some power.I then took the 2001 corolla to a certified repair facility.after having a repair shop work on the vehicles problem the technician found a crack in the intake at no. 2 cylinder.This was repaired,but the vehicle loss power as it warmed up?I replaced spark plug and plug wires and checked compression(155psi) My question is what correlation is the oxygen sensor and the loss of power to no.2 cylinder related,and what test procedure can i use to test if there is a wiring problem that is causing an injector to fail to activate and is this related to the oxygen sensor,or just giving me an inconclusive code?Your professional advice would truly be appreciated. Sincerely Jon Goldmann