Replaced exhaust, now I have no 02 sensor

[dereku]

So from my second cat back to my muffler fell off. I found it, and had an exaust shop bend me a peice to fit. But when installing that peice the second cat broke at the weld so I had to have another peice bent to replace that. I am not running with the downstream 02 sensor at all now. besides bad fuel milage, will it really effect all that much? I am not familiar with how touchy Subarus and 02 sensors are.

[ShadowGT]

From my limited experience:
You'll get crap gas mileage and really crap and unpredictable performance from the car. I'm not talking about like "can't go race" I'm saying it's going to stumble, idle bad and occasionally stall.
Then you'll have a constant CEL.

I mean when I was rebuilding my Legacy, a majority of all running issues came from a fouled downstream O2 sensor. As I understand it, the upstream O2 sensor picks up readings and the downstream O2 correlates what the upstream O2 sensor reads. The ECU makes it's adjustments by balancing the voltage readings from both O2 sensors. Without that rear O2 sensor, the ECU can't find a happy medium for proper combustion.
Correct me if I'm wrong, that's just what I noticed.

I put a brand new downstream O2 sensor in and a vast majority of performance problems went away. There is a tutorial or DIY for using a sparkplug chaser to use as a mount for a rear O2 sensor in the event you're not using the 2nd Cat converter. Long story short, drill a hole in that replacement pipe, thread the chaser in, thread the O2 sensor in and hope that works.
Of course it's not going to be perfect because that downstream O2 sensor evaluates the emissions coming from the heated up elements in the rear cat. Without that cat, you're going to get funky readings and a probably a CEL. But I guess thats better than no O2 sensor at all.

Then again I could be wrong. I just stick with the fact my car ran like hell with a bad downstream O2 sensor and then it got better with a replacement.

[dereku]

I am familiar with the non fouler trick, if I had time today I would have had a bung welded into the pipe I had made, but no time, and a broken 02 sensor left me with no choice. I might look into that but I think since I found that broken wire I have been driving the car with a non functional 02 sensor the whole time.

In the Neon world, without the downstream 02 sensor, the car will spit black and stumble and run like a peice of shit till WOT. I am glad to see the Subaru is not so dependant on it!

[rudgers73]

get one in there ASAP. You are going to burn up your cat and/or start your car on fire. Cats are expensive, and so are cars.

[ouch1011]

The pcm won't do anything to cause the cats to fail. The only thing the downstream o2 does is monitor the cat efficiency to make sure its working. Worst it will cause is a cel.

[Huffer]

get one in there ASAP. You are going to burn up your cat and/or start your car on fire. Cats are expensive, and so are cars.

Say what? A missing rear O2 will put the car into factory base map mode and more than likely - run a little rich.

[ShadowGT]

get one in there ASAP. You are going to burn up your cat and/or start your car on fire. Cats are expensive, and so are cars.

Say what? A missing rear O2 will put the car into factory base map mode and more than likely - run a little rich.

Generally, like total crap. My car was stumbling and blowing black smoke eventually stalling until I replaced that rear O2. In these cars it's not going to burn the cat. Both O2 sensors work in tandem, the rear checks the front correlating the signal to the ECU to adjust the timing and fuel trim. A lack of downstream O2 sensor will just cause a loss of signal and the car runs like caca. The cat won't overheat. It'll probably foul up faster from the increased carbon getting blown down the exhaust though.

On the other hand.. losing a bypass air hose off your air intake will cause your exhaust to heat up and glow red at the cats. I watched that happen last year.

[dereku]

So with the Neon coil I just put on I should be about even! lol, seems to be working good so far, but haven't be driving it because of a screwed wheel bearing. Hopefully getting that fixed tomorrow then I want to go out and try my outback rear sway bar I just put on. I hope the car feels a little bit more solid.

I am surprised it runs so good with only one 02 sensor, like I said, a Neon wouldn't do this.

[Grafton]

I'm running just a front O2 atm (neeed to extend wires...) doesn't seem to effect the 2.2l computer