Can you run without downstream O2 sensor?
 

I've posted another thread about needing a sensor ASAP (see message below). I had a suggestion just to plug the bung until my new sensor comes in. What would happen if I did?

I figure it would throw a CEL, but would this be all?



(MESSAGE FROM OTHER THREAD)
"So... I'm putting in a P&L header, and things are going well until I try to take the downstream o2 sensor out of the factory manifold. Talk about tight!!! I get it out and the the threads are completely stripped. I don't think it could even be re-cut to make it work.

I go to Subaru, three parts dealers and check online....no quick fix. This part is not in the USA and no one could tell me if there was something 'close' that might work. A 4-day wait is the best I could do for the part.

I put one on order, but was wondering if anyone might have an idea about possibilities in the meantime?"

You'll throw a CEL but it's the front o2 sensor that is used for closed loop fuel.

I posted my answer in your other thread.

You will have a check engine light and non-funtional cruise control

What is the function of the downstream sensor? Its it just for catalytic efficiency or is it something more?

The sole purpose of the downstream 02 is catalyst monitoring, will set a CEL, nothing more.

You need the downstream O2 or you lose lean cruise so your MPG goes to shit, like dramatically. It will not cruise at 14.7:1 if it's missing. It isn't like most cars where it's sole purpose is to detect the cat.

I did the same thing on mine and was able to use a chaser to clean it up. I replaced the sensor with this:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

$54 and shipped quick.

you can run without the rear 02, guys repurpose the rear 02 to use as flex sensor input on ecutek.

however as above you will need to disable some CEL codes associated with rear 02 and also disable its compensations in the tune else your economy will be crap when cruising and you will get cel light and no cruise control

That's not entirely true. I haven't run a rear O2 for ages. It does however default to CL at around 13.9 for about 20-30 seconds before returning to 14.7. Not sure why and if the input is re-purposed this may not happen as I suspect the ECU is looking for a voltage input.

My logs showed me going miles on the interstate without ever hitting 14.7 while mine was disconnected. Have you made other changes other then simply disabling the CELs as Steve just pointed out?

Yes I have. I've zeroed the rear O2 compensation limits.

Upstream O2 is necessary for proper AF ratio and going from open to closed loop, without it you will run rich all the time and be using more gas than necessary

Downstream O2 is only to monitor cat converter efficiency so pollutants such as NOx, CO, and HC are being converted to H20 and CO2. Without DS O2 you will get a CEL but will not affect performance, only emissions.

To the best of my knowledge this applies to most cars, unless FRS/BRZ is special

If you using romraider here are compensations to zero , similar deal on Ecutek. you will also need to disable some CEL codes as well


http://www.ft86club.com/forums/showp...78&postcount=4

I was able to get rid off all my CELs but couldn’t get it to lean cruise and it was guzzling fuel. Thanks for the details on what table needs to be changed. I will bookmark this incase I need it another day.