what does putting spacers on the post cat o2 sensor do?

 

Are you talking about something like this: (spacer is the silver part)



That's used to move the O2 sensor out of the exhaust stream to "fool" it into thinking everything's working correctly in the catalytic converter (even if the converter's not present anymore). It's the same principle as the "O2 simulators" you see on the market - basically a way to run without a cat or with a gutted cat and not throw a "check engine" light.

I don't recommend messing around with or disabling any sensors that are used to determine the air/fuel ratio in the engine, but evidently it works for some people.

 

The second sensor just keeps track of the Cat efficiency and won't affect A/F ratios.

 

Thanks for the clarification. I wasn't sure if all of the fuel metering decisions were based on the pre-cat sensor or if the post-cat sensor played a part as well.

 

yes im talking about spacers like that. i have them and i throw a cel every time i drive on the hwy till my car is warm then i get it reset and its fine

 

yo i got a question I but those spacers in from alta proformance and like a day later when i was drving on the free way i got a engine code p0136 looked it up and its says a slow 02 sensor or something like that post cat? Did i not tighten it down enough? i used graphite on the spacer threads and on the threads on the o2 sensor, could they be dirty? . I have a scan guage2 and cleared the code. Is it possible that the code will show up again ? and what actions would should i take to make sure it doesnt come on again.

 

ps i have a alta down pipe and alta full exhausts. 08 mini s. thanks

 

one more question, i noticed that in your picture your spacers are doubled, I have two spacers also. Do they go out both sensors or double on one.

 

Not my sensors - just a random picture I found to illustrate the spacers. I think the point of the double spacers is in case one spacer isn't enough to get the O2 sensor completely out of the exhaust stream.

As for your "slow O2 sensor" fault, I'm wondering if it might be because the O2 sensor isn't getting hot enough to work properly.

 

Talking about O2 sensors, I recently had to remove an 03 Hyundai downstream O2 sensor. To put it kindly, it was a PITA. I nearly yanked out the exhaust in the process. This was after penetrating oil was used, heating up the vehicle, using a hot torch, etc. I'm tempted to remove the O2 sensor on the new Clubman and make sure there's anti seize or something to make sure this does not happen to me if I need it replaced.

Anyone with experience removing the O2 sensors a few years down the road?

 

Mechanics usually have to use an impact wrench to remove them sucessfully.

 

Yea I tried to remove my post-cat sensor today with a 6-inch adjustable wrench and I stood no chance in hell of getting it loose. Going to pop's tomorrow to get some better tools!

 

This is a very good idea. I just might do this with all the bolts on the exhaust. I <3 anti-seize.