[tarlaGT0]

Hey so I'm having trouble with my f32 idling abit rough, I installed a catless downpipe a few months ago and everything was fine for a few weeks until all of a sudden a cel popped up I figured it was the o2 sensors so I read a few threads discussing how an o2 sensor spacer would fix the issue and so I bought one and slapped em on yesterday and along with a cheap Bluetooth obd2 reader I bought I cleared the codes. Since then the cel has turned off which is perfect but I noticed an issue where if I leave the car running for like a solid minute it rpms would drop to sub 1k and idle rough until the rpms picked back up within 5 secs.
It also happens when I don't press the gas and the car is just moving bc its in gear but this one is reasonable bc of the rolling resistance. Also after clearing the cel when i took it out for a test drive all of a sudden it threw up 2 errors for 1 not being able to read tpms and 2 for an "unstable chassis" which I have no idea wut it means but is the time I came to a stop the y both disappeared. Any help is appreciated.

[tarlaGT0]

Also quick question should I follow bmws work on the oil change date bc it seems kinda crazy that it says I don't need an oil change for another 8kkms

[Randy Johnson]

You did a catless downpipe without a tune? I'm not sure that would work in the long run.

With covid and the fact that I only live 2 miles from work I only drive 5-6k miles a year. I change my oil once a year at about 6k miles. I use bmw oil kit from FCP Euro. 1/3rd the cost of the dealer near me.

[BMWILUVU]

I have to ask. You put the spacer on the downstream O2 sensor only? Is the new downpipe fully secured to the turbo?

[tarlaGT0]

Originally Posted by BMWILUVU

I have to ask. You put the spacer on the downstream O2 sensor only? Is the new downpipe fully secured to the turbo?

Yes I tested the whole thing for exhaust leak after the install and took care of it all so there is no exhaust leak and the o2 sensor spacer goes on top of both o2 sensors and then gets secured to the downpipe

[tarlaGT0]

Originally Posted by Randy Johnson

You did a catless downpipe without a tune? I'm not sure that would work in the long run.

With covid and the fact that I only live 2 miles from work I only drive 5-6k miles a year. I change my oil once a year at about 6k miles. I use bmw oil kit from FCP Euro. 1/3rd the cost of the dealer near me.

I didnt do it for power gains, I did it for the sound and also for the motor to be able to breath better

[thejeremyman9]

Originally Posted by tarlaGT0

Yes I tested the whole thing for exhaust leak after the install and took care of it all so there is no exhaust leak and the o2 sensor spacer goes on top of both o2 sensors and then gets secured to the downpipe

No no no. Absolutely do not put a O2 sensor spacer or anything else on the primary O2 sensor. That sensor is critical for closed loop fueling. With a spacer, minicat, or anything else, you are totally throwing off fuel trims and the car could be dangerously lean or rich. Remove that spacer immediately.

For the secondary O2, you are also not supposed to run any kind of spacer (etc) as the secondary O2, if it behaves like it does on the N55, is used for more than just catalyst monitoring and is used to calibrate or prevent drift on the primary O2 (MHD confirmed this). So, remove that one as well. People only run these as a temporary solution to try and pass emissions with a catless (or inefficient catted) DP and they are not supposed to be ran long term.

You should removed both immediately.

[BMWILUVU]

Originally Posted by tarlaGT0

Yes I tested the whole thing for exhaust leak after the install and took care of it all so there is no exhaust leak and the o2 sensor spacer goes on top of both o2 sensors and then gets secured to the downpipe

The reason I asked is I suspected you put a spacer on the upstream O2. This throws off your AFR, you need to remove that. As far as the downstream O2, the urban myth is that its somehow used to adjust the longterm trim or calibrate the wideband which I've never been able to confirm. In fact, ISTA explicitly says that the downstream O2 does not affect AFR and is only used for catalyst monitoring. Theres a long story to this but it does not belong here.

[tarlaGT0]

Originally Posted by thejeremyman9

No no no. Absolutely do not put a O2 sensor spacer or anything else on the primary O2 sensor. That sensor is critical for closed loop fueling. With a spacer, minicat, or anything else, you are totally throwing off fuel trims and the car could be dangerously lean or rich. Remove that spacer immediately.

For the secondary O2, you are also not supposed to run any kind of spacer (etc) as the secondary O2, if it behaves like it does on the N55, is used for more than just catalyst monitoring and is used to calibrate or prevent drift on the primary O2 (MHD confirmed this). So, remove that one as well. People only run these as a temporary solution to try and pass emissions with a catless (or inefficient catted) DP and they are not supposed to be ran long term.

You should removed both immediately.

Will do asap thanks for the info rlly helped me out I was scared .aybe the cheap obd2 reader fucked with the afr

[tarlaGT0]

Originally Posted by BMWILUVU

The reason I asked is I suspected you put a spacer on the upstream O2. This throws off your AFR, you need to remove that. As far as the downstream O2, the urban myth is that its somehow used to adjust the longterm trim or calibrate the wideband which I've never been able to confirm. In fact, ISTA explicitly says that the downstream O2 does not affect AFR and is only used for catalyst monitoring. Theres a long story to this but it does not belong here.

Ye I'm just gunna take off both spacers and keep clearing codes if it throws up any I heard some ecu will learn after clearing the same code so often to a point where they won't throw that specific code anymore

[thejeremyman9]

Originally Posted by BMWILUVU

The reason I asked is I suspected you put a spacer on the upstream O2. This throws off your AFR, you need to remove that. As far as the downstream O2, the urban myth is that its somehow used to adjust the longterm trim or calibrate the wideband which I've never been able to confirm. In fact, ISTA explicitly says that the downstream O2 does not affect AFR and is only used for catalyst monitoring. Theres a long story to this but it does not belong here.

We asked MHD about this and they specifically said do not run any kind of spacers or anything on the secondary O2 because it is used for more than just catalyst monitoring. The response is buried somewhere in the MHD thread in the N55 section. There are also videos on youtube about it. It's not a myth. It does not directly affect AFR, no, as that is the primary O2 (which is a wideband). But that doesn't mean it isnt used for other functions that can affect engine performance.

[thejeremyman9]

Originally Posted by tarlaGT0

Will do asap thanks for the info rlly helped me out I was scared .aybe the cheap obd2 reader fucked with the afr

Bolded text - no, this is not a thing. The OBD2 reader does one thing - READ. It can't write unless it has flashing capabilties, so there's no way it affected anything.

Originally Posted by tarlaGT0

Ye I'm just gunna take off both spacers and keep clearing codes if it throws up any I heard some ecu will learn after clearing the same code so often to a point where they won't throw that specific code anymore

This is also not a thing... where did you hear this from? Yes, ECU's have adaptations and learn things but they absolutely do not stop throwing a code if you keep clearing it. "Keep clearing codes" is not a solution to a problem if there is one.

[WDE82]

Originally Posted by tarlaGT0

I didnt do it for power gains, I did it for the sound and also for the motor to be able to breath better

Well you're now polluting the equivalent of about 100 cars so I hope it sounds just great to everyone around you.

Anyway removing cats requires a tune or O2 sims to avoid issues. I recommend you just put the cats back and get a cat-back exhaust system instead of spewing NOx into the atmosphere like it's 1969.

[BMWILUVU]

Originally Posted by thejeremyman9

We asked MHD about this and they specifically said do not run any kind of spacers or anything on the secondary O2 because it is used for more than just catalyst monitoring. The response is buried somewhere in the MHD thread in the N55 section. There are also videos on youtube about it. It's not a myth. It does not directly affect AFR, no, as that is the primary O2 (which is a wideband). But that doesn't mean it isnt used for other functions that can affect engine performance.

What other functions? I am looking for concrete information. I can find no documentation whatsoever about an undocumented role for the secondary oxygen sensor in ISTA.

[JonOhh]

Originally Posted by tarlaGT0

I didnt do it for power gains, I did it for the sound and also for the motor to be able to breath better

If you don't want to get a tune, it's probably best to put the oem downpipe back on and modify your exhaust instead. These motors breathe just fine... actually more than fine...for stock tune.

The DME runs all sorts of tests based on those secondary O2s, which in themselves can cause a rough idle as the AFR is varied back and forth between rich and lean during some of the test procedures, which will usually continue until the test is passed...which it won't with a catless downpipe. You can sometimes clearly hear this happening at idle... doesn't feel very nice.

[Boostedphil698]

You would have been better off getting a catted downpipe from Fabspeed or Active Autowereke. It would have given no more sound and no hassle of a check engine light.

[thejeremyman9]

Originally Posted by BMWILUVU

What other functions? I am looking for concrete information. I can find no documentation whatsoever about an undocumented role for the secondary oxygen sensor in ISTA.

I already explained at a high level above - "is used for more than just catalyst monitoring and is used to calibrate or prevent drift on the primary O2 (MHD confirmed this)"

https://www.e90post.com/forums/showthread.php?t=1147379

https://blog.fcpeuro.com/faulty-oxyg...toms-diagnosis

Quote from FCP page: "The signal from the second bank of oxygen sensors is used primarily to detect any problems with the vehicle's catalyst and to tune the fuel trim. "

It's all over the internet, you can do your own searches and fact checking. Fundamentally its because the primary O2 is a wideband and the secondary is a narrowband, so the secondary is used to keep the primary "calibrated" around lambda=1.

[BMWILUVU]

Thanks for posting your information. One is an e-series forum discussion and the FCP is a blanket statement. IMO, this is heresay information from users about long-term fuel trim drift not that it should necessarily be discounted. I have not seen LTFT drift on my catless setup. Maybe this was a feature of the ECU program in the e-series. Maybe this is used in the F-series engines but not documented. ISTA does not discuss any use of downstream O2 in anything but catalyst monitoring. I still think this is important enough though to keep an eye on but I still do not see definitive proof that downstream O2 is being used in any way in fueling or calibration. In fact, the forum discusses the narrowband voltage at 1V whereas BMW narrowband baselines at .750mV. Theirs is not a technical discussion meshing with reality of what ISTA is stating. I am going to dig somewhat further including asking FCPEURO where they got their information. Thanks.

Originally Posted by thejeremyman9

I already explained at a high level above - "is used for more than just catalyst monitoring and is used to calibrate or prevent drift on the primary O2 (MHD confirmed this)"

https://www.e90post.com/forums/showthread.php?t=1147379

https://blog.fcpeuro.com/faulty-oxyg...toms-diagnosis

Quote from FCP page: "The signal from the second bank of oxygen sensors is used primarily to detect any problems with the vehicle's catalyst and to tune the fuel trim. "

It's all over the internet, you can do your own searches and fact checking. Fundamentally its because the primary O2 is a wideband and the secondary is a narrowband, so the secondary is used to keep the primary "calibrated" around lambda=1.

[AndrewGAmin]

Originally Posted by tarlaGT0

I didnt do it for power gains, I did it for the sound and also for the motor to be able to breath better

For better sound take of the silencer not the downpipe and without a tune your engine is not running efficiently anymore , but more laggy

[thejeremyman9]

Originally Posted by BMWILUVU

Thanks for posting your information. One is an e-series forum discussion and the FCP is a blanket statement. IMO, this is heresay information from users about long-term fuel trim drift not that it should necessarily be discounted. I have not seen LTFT drift on my catless setup. Maybe this was a feature of the ECU program in the e-series. Maybe this is used in the F-series engines but not documented. ISTA does not discuss any use of downstream O2 in anything but catalyst monitoring. I still think this is important enough though to keep an eye on but I still do not see definitive proof that downstream O2 is being used in any way in fueling or calibration. In fact, the forum discusses the narrowband voltage at 1V whereas BMW narrowband baselines at .750mV. Theirs is not a technical discussion meshing with reality of what ISTA is stating. I am going to dig somewhat further including asking FCPEURO where they got their information. Thanks.

I understand the sources i grabbed (from what i had handy) were somewhat based on E-series. This is by no means a comprehensive list of documentation on the internet, just the ones i recalled looked at some time ago when i did a quick search. I would encourage you to do further research specific to F-series and report back. I would also note that this question was specifically asked to MHD support in response to using a spacer on the downstream O2 and the response was posted in the F3x N55 technical forums MHD thread, i would just have to dig through that since it was probably over a year ago. I fully support your fact checking and confirming applicability to our cars. Also, being catless has nothing to do with it. It's about putting a spacer, minicat, O2 sim, or anything else that would give false/modified readings to the secondary O2 (or, running without one). I think the forum discussion was just that NBO2s are 0-1 whereas widebands are 0-5V (nominally, at least).

[BMWILUVU]

Originally Posted by thejeremyman9

I understand the sources i grabbed (from what i had handy) were somewhat based on E-series. This is by no means a comprehensive list of documentation on the internet, just the ones i recalled looked at some time ago when i did a quick search. I would encourage you to do further research specific to F-series and report back. I would also note that this question was specifically asked to MHD support in response to using a spacer on the downstream O2 and the response was posted in the F3x N55 technical forums MHD thread, i would just have to dig through that since it was probably over a year ago. I fully support your fact checking and confirming applicability to our cars. Also, being catless has nothing to do with it. It's about putting a spacer, minicat, O2 sim, or anything else that would give false/modified readings to the secondary O2 (or, running without one). I think the forum discussion was just that NBO2s are 0-1 whereas widebands are 0-5V (nominally, at least).

Yes and I do know other manufacturers are using the downstream in more than catalyst monitoring in their ECU logic but I've not found such in BMW documentation as yet and it could be series dependent. If you find the MHD information, it would be helpful for us catless people.