Looking at the setup on an S197. Why did ford put the up stream driver side O2 sensor up on the exhaust manifold and not on the down pipe like the passenger side??? Kind of stupid if you ask me.

 

Seems unusual. Only time that would make sense to me is for more accurate EGT monitoring. Unless that happens to be the case.

 

Yeah, I'm thinking about upgrading my cats to metallic free flowing and I was thinking. If I had to ever replace the one upstream O2 sensor on the driver side, it would be next to impossible to do without removing the header. Which I won't do, I'll just weld in a new O2 bong just ahead of it in on the down tube.