Originally Posted by Pilsner Pig
Very good question. I thought the same and when I swapped in a 1.6L the header did not have a spot for the O2 sensor so I obviously didn't install it. So far it runs like a charm!
Thanks again PP. It must not be TOO important then.
I found online PDF copies of a 1988 Samurai service manual (maybe from a link here... been too many Sammi sites to remember exactly) and was reading through it an hour or two ago. What I learned is the ECM controls a solenoid in the carb, cycling it 16 times per second. When it goes down (ECM signal) it opens an air passage making the mixture go lean. No signal makes it go back up and rich.
I've had other vehicles that performance improved with a new O2 sensor if the one it replaced had over 60,000 miles. The one in our Sammi is probably original (180,000 miles) and since it's easy to get to I was considering installing a new one.
From your experience it seems the ECM has a pretty good "default" program. Do you have to smog yours?
As part of the condition of sale, I had the seller smog this one but I know enough about engines to also know that it couldn't have legally passed the visual test. Which makes me wonder about the sniffer test. For our off-road-only use I won't need it to pass smog again, but as cheap as O2 sensors (usually) are, it seemed like a cheap & easy "performance" upgrade.
So I coulda/shoulda found that manual before posting here, but if I'd done that you wouldn't have told me how well it runs with NO sensor.