backfire

Hello everyone, I'm new to the forum,This is my fourth Jeep. I have been working on a body of frame project for Almost two years now. I have the body back on engine and drivetrain hooked up and harnesses and grounds connected. The problem I am having is starting. I will list all the information...

I know its for the upstream O2 sensor. But i was wondering if that would cause backfire and stalling.