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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > Do I need secondary 02 Sensors?



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      01-01-2014, 09:55 PM   #1
Tim603
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Do I need secondary 02 Sensors?

If I have the tune to eliminate the emissions codes thrown by catless headers Do I still need secondary 02 sensors?

Arent the secondary 02 sensors just there for emissions purposes?

Supposes I had one secondary 02 sensor plugged in just not screwed into the exhaust (just set off to the side), would this work or does it need to be in the flow of the exhaust?

Thanks for any input guys

BTW this is for N52 I just wanted to see if any of you N54 guys had any input on this matter
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      01-01-2014, 09:58 PM   #2
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You must have the secondary O2 sensor for the car to run correctly.
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      01-02-2014, 09:34 AM   #3
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You must have the secondary O2 sensor for the car to run correctly.
Why?

Unless BMW has invented magic cats secondary O2 sensors are not needed. If you leave them plugged in they will probably still throw codes because they won't warm up. But you said you had a tuner that can ignore/auto clear those. Narrow band O2's are used pre cats to measure stoic/lambda the ECM then compares that signal with the reading from post cat sensors and it determines the Cat efficiency and flags if it does not meet emissions compliance.
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      01-02-2014, 11:33 AM   #4
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Why?

Unless BMW has invented magic cats secondary O2 sensors are not needed. If you leave them plugged in they will probably still throw codes because they won't warm up. But you said you had a tuner that can ignore/auto clear those. Narrow band O2's are used pre cats to measure stoic/lambda the ECM then compares that signal with the reading from post cat sensors and it determines the Cat efficiency and flags if it does not meet emissions compliance.
The tune clears the emissions code, I will try and unplug it completely and see if it throws any
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      01-02-2014, 11:34 AM   #5
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Do the secondary 02 sensors not affect the AFR's?
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      01-02-2014, 11:38 AM   #6
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Do the secondary 02 sensors not affect the AFR's?
As I understand it, they primarily monitor the efficiency of the cats but may have a very slight effect on long term fuel trim.

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      01-03-2014, 12:30 AM   #7
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I'm going to need new 02 sensors. I have the worst gas mileage in history. Consecutive 12.4 mpg
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      01-03-2014, 01:32 PM   #8
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I'm going to need new 02 sensors. I have the worst gas mileage in history. Consecutive 12.4 mpg
Wow! Are you using e85? On 60% E85, I'm still getting right around 15 mpg with mostly city driving.
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      01-03-2014, 01:37 PM   #9
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That doesn’t sound too nutty if you have some E85 in the tank. If you spend the majority of your time starting and stopping one block to another (every single day in DC), you won’t average much more than 15/gal max. 14 gallon tank in my 1er gets me about 200 miles; daily commute is slogging through the District.
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      01-03-2014, 04:39 PM   #10
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Wow! Are you using e85? On 60% E85, I'm still getting right around 15 mpg with mostly city driving.
Nah man I only use 93 octane. I guess I should pay attention to the codes that pop up on the jb4. Every time the check engine light pops on, I read the code which is two o2 related problems and then I erase them. Now I see the results of my foolish ways
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      01-03-2014, 07:07 PM   #11
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Nah man I only use 93 octane. I guess I should pay attention to the codes that pop up on the jb4. Every time the check engine light pops on, I read the code which is two o2 related problems and then I erase them. Now I see the results of my foolish ways
Oh yeah don't ignore 02 sensor codes. I had those codes, so I replaced all 4 02 sensors, and they haven't come back.
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      01-03-2014, 07:25 PM   #12
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Replace the relevant o2s if you are getting codes, they take a lot of heat and fail/crack with frequency. I've replaced both rears on my 1er, both fronts on my E90.

Especially if it's the narrowband o2, you really don't want to be driving a lot with that. You'll have some silly AFRs.
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      01-03-2014, 08:45 PM   #13
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Quote:
Originally Posted by Ingeniator View Post
Why?

Unless BMW has invented magic cats secondary O2 sensors are not needed. If you leave them plugged in they will probably still throw codes because they won't warm up. But you said you had a tuner that can ignore/auto clear those. Narrow band O2's are used pre cats to measure stoic/lambda the ECM then compares that signal with the reading from post cat sensors and it determines the Cat efficiency and flags if it does not meet emissions compliance.
Is performance affected/timing pulled etc., or just codes thrown?
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      01-04-2014, 02:02 PM   #14
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Narrow band O2's are used pre cats to measure stoic/lambda the ECM then compares that signal with the reading from post cat sensors and it determines the Cat efficiency and flags if it does not meet emissions compliance.
Maybe this was just a typo..... but the N54 uses wideband pre-cat (control) oxygen sensors. The post-cat sensors are regular narrow band 02 sensors.
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      01-04-2014, 10:32 PM   #15
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Maybe this was just a typo..... but the N54 uses wideband pre-cat (control) oxygen sensors. The post-cat sensors are regular narrow band 02 sensors.
Interesting. I don't profess to be an N54 expert. I mostly have JDM and V8 experience. If we use wideband in the front are they Bosch or NGK sensors. I'm surprised not many OEM's use wideband because they are not needed for everyday engines as they can adjust the known maps easily in the cheaper narrowband range and wideband typically are not as robust leading to premature failure.
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      01-04-2014, 11:07 PM   #16
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Is performance affected/timing pulled etc., or just codes thrown?
I didnt think that any performance was affected but I ended up welding a new bung onto my catless headers and once the o2 sensor was inserted all the codes have gone away (thus far, crossing fingers) and it seems to be responding better. Long story short, you need secondary o2 sensors in the exhaust stream. I tried every way around it and all my car did was throw codes
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      01-04-2014, 11:25 PM   #17
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Quote:
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I didnt think that any performance was affected but I ended up welding a new bung onto my catless headers and once the o2 sensor was inserted all the codes have gone away (thus far, crossing fingers) and it seems to be responding better. Long story short, you need secondary o2 sensors in the exhaust stream. I tried every way around it and all my car did was throw codes
Thanks, any pics of the bung?
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      01-04-2014, 11:32 PM   #18
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Thanks, any pics of the bung?
you know i almost took some pics at the exhaust shop but this time of year there is snow, slush and water dripping everywhere so I didnt bother. If I take some tho Ill post them!
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      01-04-2014, 11:33 PM   #19
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Quote:
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I didnt think that any performance was affected but I ended up welding a new bung onto my catless headers and once the o2 sensor was inserted all the codes have gone away (thus far, crossing fingers) and it seems to be responding better. Long story short, you need secondary o2 sensors in the exhaust stream. I tried every way around it and all my car did was throw codes
Looks like the cross reference shows they are bosch wideband. That is a pretty sweet finding. This also means they probably use the rear sensor to help calibrate the front wideband. Which would explain why issues occur when not running them overtime.
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      01-04-2014, 11:36 PM   #20
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you know i almost took some pics at the exhaust shop but this time of year there is snow, slush and water dripping everywhere so I didnt bother. If I take some tho Ill post them!
Cool, thanks!
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      01-05-2014, 12:29 AM   #21
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The secondary sensors help keep the primaries calibrated... you need them even with dps.
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      01-05-2014, 02:10 AM   #22
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Looks like the cross reference shows they are bosch wideband. That is a pretty sweet finding. This also means they probably use the rear sensor to help calibrate the front wideband. Which would explain why issues occur when not running them overtime.
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