Are O2 sensors really necessary?

[Minderbinder3]

So I recently bought a 2000 TJ with 2.5 and as I have been poking around underneath and changing fluids I noticed that the O2 sensors have been disconnected. It lived previously out on a hunting lease and my guess was they didn’t want to fool with replacing them so they just cut the wires.

Where I live there aren’t any emissions tests and there isn’t a CEL. The engine runs like a top and seems to get decent (for a TJ) gas mileage.

Are the O2 sensors really necessarily and how did the PO bypass the CEL?

 

[Chris]

There’s a chance he just used a tuning program such as HPTuners to disable the O2 sensor circuit.

You can get by just fine without them.

 

[Brianj5600]

I would at least run the upper O2. The engine will be much happier in closed loop.

 

[Brianj5600]

I would at least run the upper O2. The engine will be much happier in closed loop.

 

[NashvilleTJ]

I would at least run the upper O2. The engine will be much happier in closed loop.

I would at least run the upper O2. The engine will be much happier in closed loop.

X2…

 

[Brianj5600]

Or is it x four? I work in an industrial cave and sometimes service is iffy leading to double post.

 

[Rickyd]

Air fuel ratio is overrated.....

 

[ItchyDong]

I would at least run the upper O2. The engine will be much happier in closed loop.

Unless it's tuned (which I highly doubt), that engine will never see closed loop without functional 02's. She's just dumping a ton of fuel down the pipe in an attempt to save herself from running lean with a blindfold on.

Yes, 02's are important. And also, running rich like that for too long will also kill your cats. Your cats need oxygen (lean) and carbon (rich) to survive, hence the switching seen by a properly functioning o2 sensor. You aren't getting any oxygen to your cats by running it like that.

 

[Jerry Bransford]

X2, no "tune" or aftermarket chip is going to allow a TJ engine to run well or even properly without the upstream 02 sensor(s).

 

[Brianj5600]

I don't know why someone would mess with closed loop. I don't think the ECM is capable of tuning closed loop. When load and RPM goes up the ECM goes to open loop. When it goes to open loop is when engine is working hard and that is when you can tune. Timing is where most of the gains come from. I think Jezza said there a little power to gain on fuel, but not much.