How many O2 sensors does a Buick Lacrosse have?

The Lacrosse will have 4 sensors. One on each set of 3 cylinders before the catalytic converter, and one after each catalytic converter. As far as your concern, a misfire is not related, typically, to oxygen sensor performance. So, please focus elsewhere on then proper root cause. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops