[SlowE92]

Bought an e92 335i with 30k miles on it. The previous owner had put catless downpipes on the car but did not plug in the post cat 02 sensors. I can actually see them dangling from the bottom and scraping the road underneath. I don't have MHD logging yet so I cant view the fuel trims and I have new 02 sensors coming in but I guess my question is, can I continue to drive the car for a week or so until I get these? This is currently my only car I have to get me to and from work.

Edit: Would resetting adaptations help short term?

[Mrmigs2011]

I think you need all o2 in for just downpipes.

The post o2 calibrate the pre o2! Without them your car will not have any accurate fueling info! Don't drive until sorted.

[chaltau]

Originally Posted by Mrmigs2011

The post o2 calibrate the pre o2! Without them your car will not have any accurate fueling info!

Where did you get this info? Sorry, this is the first time I have heard about it, or is it specific to BMW?

Post-cat O2 does only one job, which is to determine CAT health. That is it. They are typically narrow band.

Pre-cat O2 controls the trim/lambda calculation and is responsible for running the car as close to stoich as possible. They are typically wide band.

They operate independently.

OP, you should be fine driving w/o post-cast o2 for a while, as long as they are not dragging ha ha.

Most likely the previous owner disconnected it so that it won't throw emission code. Disconnecting is effectively doing the same thing as installing spacer/cheaters on them. The sensor does not see the exhaust gasses.

[chaltau]

Another thing OP, if you don't have CAT, you are wasting money on new post-cat o2.

About the pre-cat one, how do you know existing one is not working? They typically last the lifetime of car, or least 100k miles.

[Sgop335]

yes all O2 sensors are needed even for Catless, Mr migs is correct about the rear being used reference. Otherwise O2 codes will show, unless the oxygen sensor code is suppressed in the tune, which usually is not the case. If o2 sensor codes are suppressed in the tune, the Oxygen Sensors will not show Ready state for emissions.
Only cat efficiency codes are suppressed for catless.

[chaltau]

Oh yes, I am not debating the necessity of having them. The car computer should still see them as connected. It's just that the business end of them does not see any foul gases and report to the ECU

I was only questioning the need to replace old ones.

Also, Mr migs is wrong about them being used as reference for stoich calculation (correct me if I am wrong), and they will definitely throw emission code (if no CAT present) as that is exactly what they are used for. I mentioned that in my earlier post.

[Mrmigs2011]

Originally Posted by chaltau

Oh yes, I am not debating the necessity of having them. The car computer should still see them as connected. It's just that the business end of them does not see any foul gases and report to the ECU

I was only questioning the need to replace old ones.

Also, Mr migs is wrong about them being used as reference for stoich calculation (correct me if I am wrong), and they will definitely throw emission code (if no CAT present) as that is exactly what they are used for. I mentioned that in my earlier post.

No sorry I don't believe I am,

The narrowband are the main 1.0 reference for the wideband, this is documented by bimmerprofs and so far everything they've explained about the n53 has been true to the n54 as well. I believe most cars run this setup now and it makes sense given the wide range the wideband has to function at.

The car won't run true unless all sensors are functional or have been specifically coded out. However it should still run without them but to what degree of health I'm not sure.

[SlowE92]

im mhd tage 2 and it still throws codes for both post cat 02 sensors.

[Mrmigs2011]

Originally Posted by MakoB96

im mhd tage 2 and it still throws codes for both post cat 02 sensors.

I'm mhd stage 2 with DPS and show no codes for o2, did you reinstall them?

[SlowE92]

Originally Posted by Mrmigs2011

I'm mhd stage 2 with DPS and show no codes for o2, did you reinstall them?

No they're dangling off the downpipes lol. I ordered new ones but previous owner installed downpipes and never plugged them in. I tried running the tune to see if it would suppress them and they didn't.

[SlowE92]

Originally Posted by Mrmigs2011

I'm mhd stage 2 with DPS and show no codes for o2, did you reinstall them?

Everytime I reset adaptations it runs great looking at the logs but after 50 or 60 miles it starts to run lean. After I reset adaptations it runs fine again. So I've just made it a habit to reset adaptations every 30 miles or so.

[Sgop335]

Need the post o2 sensors!
Mhd doesnt suppress those...