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Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > 3 Series / 4 Series > E36 (1991 - 1999)

E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 05-13-2015, 07:11 PM
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Im confused about oxygen sensors?!

Hey guys im having a bit of trouble understanding this O2 sensor situation going on. So I didn't pass smog. I got the results and showed One of my friends that works at a custom exhaust shop and he said that I should change the rest of my oxygen sensors because it's causing my car to burn too much fuel. He said this after he saw the results of the smog sheet. I have told him that I had changed one of the oxygen sensors before and so I have one new one installed for about 5 months. Now I don't really remember which one I changed exactly but I think it was the oxygen sensor before the catalyst on the exhaust manifold. I think it was the bank 3. So I'm looking up oxygen sensors online but it only shows one for my car, are they all the same? Click image for larger version

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  #2  
Old 05-13-2015, 07:15 PM
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I can guarantee you didn't change a bank 3 sensor since your 328i only has bank 1 and bank 2.

There are two pre CAT O2 sensors and 2 post CAT O2 sensors, one each for bank 1 and bank 2.
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Old 05-13-2015, 07:23 PM
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Quote:
Originally Posted by dc_wright View Post
I can guarantee you didn't change a bank 3 sensor since your 328i only has bank 1 and bank 2.



There are two pre CAT O2 sensors and 2 post CAT O2 sensors, one each for bank 1 and bank 2.

Haha well then it must have been the pre CAT bank 2 O2 sensor that i changed. So which are the ones in the picture?
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Old 05-13-2015, 07:26 PM
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post cat sensors do nothing for fuel trim/emissions. they are only there to check the efficiency of the cat.


what are the results of your tests??





df
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Old 05-13-2015, 10:08 PM
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Originally Posted by drivinfaster View Post
post cat sensors do nothing for fuel trim/emissions. They are only there to check the efficiency of the cat.





What are the results of your tests??











Df

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Old 05-14-2015, 04:26 AM
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It's times like this when all I can say is OBD1 FTW! Well that and I'm supper glad that I live in a state that doesn't care if your car can't pass a smog. I do however feel your pain as I spent most of my life in California.

Good luck with your emissions kind sir, I hope it doesn't end up costing too much.

Also keep in mind that too much raw/unburned fuel can also be from things like carbon buildup on the valves, bad miss gapped spark plugs, weak coils, bad fuel pressure regulator, or even a clogged air filter. Or it could be a faulty O2 sensor. Also make sure you are running the proper octane fuel. Cheap lower quality, or low octane fuels do not burn as completely as the good stuff.
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Old 05-14-2015, 05:55 AM
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As the others have noted. You want to ensure your Pre CAT 02s are good. However with those results you should have had the check engine light illuminating. Was it on and if so can you list the codes?
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Old 05-14-2015, 04:07 PM
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Originally Posted by 66 6 View Post
As the others have noted. You want to ensure your Pre CAT 02s are good. However with those results you should have had the check engine light illuminating. Was it on and if so can you list the codes?

Nope check engine light is off
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Old 05-14-2015, 04:07 PM
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Quote:
Originally Posted by MsMuse View Post
It's times like this when all I can say is OBD1 FTW! Well that and I'm supper glad that I live in a state that doesn't care if your car can't pass a smog. I do however feel your pain as I spent most of my life in California.

Good luck with your emissions kind sir, I hope it doesn't end up costing too much.

Also keep in mind that too much raw/unburned fuel can also be from things like carbon buildup on the valves, bad miss gapped spark plugs, weak coils, bad fuel pressure regulator, or even a clogged air filter. Or it could be a faulty O2 sensor. Also make sure you are running the proper octane fuel. Cheap lower quality, or low octane fuels do not burn as completely as the good stuff.

Thank you! Im using 89 gas right now
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Old 05-14-2015, 07:41 PM
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your free o2 is *way* high.......the cat is not retaining or using it, otherwise your hc would be reduced to co, and the co would be further reduced to lower the nox.

i agree, you should have some codes for something...fuel trim threshold, o2 sensor signal or cat efficiency code(s),

again, without looking at the fuel trim and live gasses, you could also be having a lean misfire, but you state there are no issues with the way the car performs.

a top engine clean/decarbon service would probably help some, but it will most likely not affect the emissions enough to allow it to pass.





df
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Old 05-14-2015, 09:45 PM
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Quote:
Originally Posted by drivinfaster View Post
your free o2 is *way* high.......the cat is not retaining or using it, otherwise your hc would be reduced to co, and the co would be further reduced to lower the nox.



i agree, you should have some codes for something...fuel trim threshold, o2 sensor signal or cat efficiency code(s),



again, without looking at the fuel trim and live gasses, you could also be having a lean misfire, but you state there are no issues with the way the car performs.



a top engine clean/decarbon service would probably help some, but it will most likely not affect the emissions enough to allow it to pass.











df

Ya there are no codes, my car feels a bit slow but its probably because i got used to its power haha.
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