Moving o2 sensor closer to engine

[BackroadBomber]

On my 03 civic ex, in stock form, there’s no o2 sensor on the exhaust manifold. There’s one on the down pipe shortly after the flange, and the catalytic converter is underneath the car with the second sensor screwed onto the back of it. The previous owner replaced the stock manifold with a cheap stainless eBay header. It’s made for several applications, so it has a plugged o2 sensor bung on it. This weekend my catalytic converter decided to rot out and snap in half. The replacement has a plugged bung where it’s supposed to be, right after the flange. I would’ve never messed with it, but as long as i have to remove the o2 sensor anyways, would it be at all beneficial to move it to the header? It would be about 8” closer to the engine. The lower trim level civics have the catalytic converters built right into the manifolds, and the upstream sensor on them are much closer to the exhaust ports, so I’m not really concerned about too much heat or anything. I was thinking maybe it would make the sensor heat up slightly faster to get the car out of rich-running “warm up mode,” or possible the extra heat would then in turn trick the cars computers into making it run slightly leaner? Maybe it will do absolutely nothing and its just wishful thinking? Sadly I’m replacing with a higher-flowing cat, so any gains this next tank could not be 100% contributed to this. I was just wondering what y’all think.

[cRiPpLe_rOoStEr]

Originally Posted by BackroadBomber

Maybe it will do absolutely nothing and its just wishful thinking?

Most likely wishful thinking. On a sidenote, I noticed that Honda motorcycles often have the O2 sensor closer to the exhaust port, compared to motorcycles of other manufacturers, but maybe its major benefit is keeping more protected from road debris...

[Blacktree]

I assume you're talking about moving the upstream O2 sensor? Because the downstream one obviously needs to remain downstream of the catalyst. Anyway, moving the upstream sensor a few inches further upstream may not make a noticeable difference. But I guess it wouldn't hurt to try it and find out.

[Ecky]

I'd wager no difference, unless perhaps the O2 sensor bung is on one of the individual tubes, before the collector. In which case you're getting a reading from one cylinder, rather than an average.

[oil pan 4]

The engine controla may go closed loop a few seconds sooner.

[cRiPpLe_rOoStEr]

Originally Posted by Ecky

In which case you're getting a reading from one cylinder, rather than an average.

I have only seen O2 sensors on individual tubes on motorcycles, usually some parallel-twin with one O2 sensor for each cylinder or some other motorcycles with dual exhausts.