N54 cats and 02 sensors

fmorelli

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I wanted to share a bit of exhaust info. My car is running with DPs and a custom exhaust. That exhaust runs 49 state legal high flow cats in the mid pipes only. We relocated the post-cat 02 sensors to a bungs at the rear of those mid-pipe cats, using a vibrant j-pipe as we had little tunnel room. I have no 02-related codes on my car (going on 7k miles) and I just blew clean through a test facility to renew tags. This is not a common setup from what I've read, but it works and allows the car to be mostly legal, at least in the intent of cats. For others thinking about exhaust ...

Filippo

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Erichale77

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I'm curious as to how accurate your readings are with that placement design. Looks nice and tidy but sensors are not in exhaust flow but rather in a bung pocket. But if that all that's needed then great. I'm running single so post cat sensors not as important.
 

veer90

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I'm curious as to how accurate your readings are with that placement design. Looks nice and tidy but sensors are not in exhaust flow but rather in a bung pocket. But if that all that's needed then great. I'm running single so post cat sensors not as important.

That placement probably actually helps the car not throw any O2 / cat codes lol. If it's just a bung and not a venturi, AFRs will definitely be affected.

I just disable all emissions codes in my tune and take it to my friend's shop for inspection, mostly for tints (it will pass OBD inspection at any station in NY). No sniffer and they can't prove anything without looking under the car.
 

fmorelli

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I just passed a sniff test (not OBD2 plug test). Downpipe cats are simply for cold emissions as they heat up and do the job faster. For 99% of operation, mid-pipe cats do the necessary emissions work. IMHO one can have cake and eat it too. And yes the j-bung certainly would help the post-cat say all is fine, but we did it because of space issues.

Filippo
 
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RSL

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I have high flow catted DPs and from my testing, the earlier the rom, the more sensitive it is for tossing cat efficiency codes. IJE0S will throw a code on them before I even get out of the garage, IKC0S takes maybe 10-20 miles IIRC. I've never had a code on INA0S in the almost 4 years they've been in though. Efficiency tolerances are only part of the story though, no issues with AFRs/trims/fuel modes with them placed like that? How long have you had it setup like that?
 

fmorelli

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I am on INA0S. We are talking post-cat 02 sensors so that sensor data has nothing to do with AFR/trims/fuel if I understand correctly? post-cat is only a catalyst efficiency function.

Been like this for 2 years and 7k miles. I had a few weird timing codes at the beginning that disappeared after adaptation reset. Never saw them again.

Filippo
 

RSL

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That's one of those things that spread early on with N54, but things in the many years since point to them having a role in the O2 loop/feedback process, not just looking to see if cats are working. There's no real reason to think they wouldn't be included in the feedback loop. They can certainly monitor what's going on post conversion and provide feedback to the DME on a finer scale from what should be a clean(er) sample.

Not sure if I can dig any examples up quickly, but @jyamona might be able to just confirm off the top of his head.

That's great if it's not having issues and it's probably not that big a deal in the first place. I'd expect it to carry a lot less weight and/or take a lot longer to move anything enough to be a problem. An adaptation reset may be all that's needed to restart the slow-moving clock if it becomes one, but that doesn't always seem to be a fix.
 
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jyamona

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The rear o2's are also used to age and adapt the characteristic curve of the main lambdas (very important). They are 100% required (at least 1 if you are ST w/ a single downpipe /mid-pipe)
 
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fmorelli

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Well damn. Learn something new every day, @jyamona. Not sure why the distinction to ST. I'm sure the j-bungs give the post cats diminished exhaust sampling. Any speculation on what effect that has with twins?

I thought sensor voltage to a/f ratio was a static graph relationship and, (aside from heaters going south) was something that degraded and ultimately went out of range and set a code (to be replaced).

Filippo
 

jyamona

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I thought sensor voltage to a/f ratio was a static graph relationship

That's how it starts out, but over time BMW attempts to extend this with sensor aging (from rear o2 feedback). It adapts the characteristic curve. However, this is also has a limit, and once exceeded will throw the codes.

Not sure why the distinction to ST.

ST cars can run in "single rear o2" mode with a few config flags in the XDF. This lets you remove the bank 2 rear o2 and run a standalone wideband (or just plug it) in it's place w/o having to add another bung. Also one less sensor to replace over time.
 
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fmorelli

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That's how it starts out, but over time BMW attempts to extend this with sensor aging (from rear o2 feedback). It adapts the characteristic curve. However, this is also has a limit, and once exceeded will throw the codes.
Thank you for the explanation. I would wonder about the effectiveness of a strategy of using one sensor with relative readings. Thankfully my car will never see old sensors so I'm probably fine. That's good info, though, I would have never guessed.

Filippo
 

jyamona

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Thank you for the explanation. I would wonder about the effectiveness of a strategy of using one sensor with relative readings. Thankfully my car will never see old sensors so I'm probably fine. That's good info, though, I would have never guessed.

Filippo

I am debating adding some toggles in the XDF to stop the rear o2 from influencing the characteristic curve over time as I imagine the logic is flawed as soon as one removes the cats. Maybe at the same time as when ST users can move their main lambdas to the downpipe :)
 

fmorelli

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doublespaces

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I bought these December 2017 as an impulse buy. Still don't know if they work or not:

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fmorelli

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They work typically with efficiency oxygen sensors, when you want them not to sniff so much exhaust. Cheap fix to replacing a cat. But that said @jyamona 's point (Post #12 above) is the stupid efficiency sensor is now being use to fudge the upstream 02 sensor's readings ... which is likely not the best thing for us.

Filippo
 

Rob09msport

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Figures I cut my secondary cats out and then read this fml in jayoma should I do a setup like fillipo or as long as my o2s aren't throwing codes I'm good and last do we need to register new o2s like battery lol
 

Rob09msport

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@fmorelli I used a 2.2k then a 10k to ground as per original vishnu dp fix only diff is I kept the legs seperate so I built 2 fixes and grounded to pin 23. Also I remember seeing on logs at steady state cruise the dme will start cycling injectors off and messing with afr this I believe jayoma said was to provide calibration data so i would assume a narrow band and wide band in succession to provide redundancy along with metered changes in fuel could easily provide data to somewhat tune the sensors.
 

fmorelli

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I'd like someone to explain how BMW uses one set of aging sensors to calibrate another set of aging sensors. But that said I went digging ... https://patentimages.storage.googleapis.com/fa/ff/49/dcdbad8dfc40d6/US8499752.pdf

The ability to short out that logic would be useful.

BTW, @jyamona, I know folks say it frequently, but thanks again for all you do for this platform.

Filippo
@jyamona any chance you can short this out? Seems like stock logic should be in play when "catted DP/OEM" is in play, but removed when running another config. Even with guys like me with post cat 02 sensors ... we moved them so whatever the calibration is would be highly suspect.

Filippo
 

jyamona

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@jyamona any chance you can short this out? Seems like stock logic should be in play when "catted DP/OEM" is in play, but removed when running another config. Even with guys like me with post cat 02 sensors ... we moved them so whatever the calibration is would be highly suspect.

Filippo


You mean remove the rear o2 influence from the main lambdas? I'm sure I could, however I am unsure if I would/should. They perform a self check on one another, and for most is a good indicator of when SOME o2 sensors are in need of replacement.

The only scenario I would feel comfortable having the rear o2 checks on main lambdas removed would be if the user also had a standalone wideband AFR gauge. Otherwise, you have no clue if the 14.7 AFR you are logging in MHD is a true 14.7AFR.
 

Rob09msport

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@jyamona any chance you can short this out? Seems like stock logic should be in play when "catted DP/OEM" is in play, but removed when running another config. Even with guys like me with post cat 02 sensors ... we moved them so whatever the calibration is would be highly suspect.

Filippo
Self check should be very easy during fuel cut and coast and then turning on Injectors in known quantity which I assume is the self check jayoma refers to