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E36 M3 (1992-1999) {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999


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Old Thu, Dec-07-2017, 01:29:27 PM   #11
M-technik-3
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Default Re: Smog Fail. Tried previous M3F solutions... Stuck. What next?

No mention of how old the oil is? Or did I miss this? I have not been under a 323i in sometime do they have the same down pipes as a 328i/M3 if so the adding dual cats has to help the car breath and but the O2 sensors will be off seems you would have to flash the ECU to let it know where they are.

2.5L M52 has one post O2 sensor and not two correct?
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Old Thu, Dec-07-2017, 10:24:44 PM   #12
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Default Re: Smog Fail. Tried previous M3F solutions... Stuck. What next?

agreed Mtech. Suspect O2's are not happy with changed exhaust and O2 bung placement.

Probably causing AFR issues....... and emissions issues.

Either reflash.... OR put stock pipe back on.
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Old Thu, Dec-07-2017, 10:53:50 PM   #13
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Default Re: Smog Fail. Tried previous M3F solutions... Stuck. What next?

Those numbers indicate the catalysts are not functioning at all, either due to insufficient temperature or something else.

High numbers for one species but not others would indicate lean (high NOx)/rich (high HC) AFR conditions.

You say you've tried different sets of cats and the car still fails. That's....odd. I would put the O2 sensors back in their original locations and try again, with blazingly hot cats (like, 2nd gear redlining hot). Try that, then reassess.
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Old Fri, Dec-08-2017, 04:19:05 AM   #14
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Default Smog Fail. Tried previous M3F solutions... Stuck. What next?

Quote:
Originally Posted by M-technik-3 View Post
No mention of how old the oil is? Or did I miss this? I have not been under a 323i in sometime do they have the same down pipes as a 328i/M3 if so the adding dual cats has to help the car breath and but the O2 sensors will be off seems you would have to flash the ECU to let it know where they are.

2.5L M52 has one post O2 sensor and not two correct?


Correct, the OBDII 2.5l 323 has a single pre-cat and single post-cat sensor in a single pipe catalyst section.
Using the the OBDII dual pipe 328/M3 catalyst section without a merge may be an issue as the single sensor that has been relocated in the head pipe ‘sees’ less total flow and hotter gases. The single post-catalyst sensor also only ‘sees’ half the gas output as it would in a single pipe.

Temporary single pipe catalyst usage may not yield enough time for re-adaptation to occur.

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Last edited by bluptgm3; Fri, Dec-08-2017 at 04:22:35 AM.
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Old Tue, Dec-12-2017, 03:34:37 AM   #15
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Default Re: Smog Fail. Tried previous M3F solutions... Stuck. What next?

Thanks again for all the responses.

Oil is fresh, sensors are fresh. I guess I can understand why the ECU of the 323 wouldn't like to have readings being sent to it from only one of the pipes of the current S52 exhaust.

However, no response yet explains the original problem of why the original exhaust with an OEM catalytic converter failed at 90k miles and clogged so bad that I could barely make it up the hill home. All without a check engine light, OBC error... nothing. This is a car that has been maintained and driven respectively, in really amazing condition throughout. Just a head scratcher really. All the research I've done says that cats don't just fail, they go bad from something upstream happening or operating not the way it's supposed to, in turn killing the cat from making it work to death.

I figured at the time when the 323 exhaust clogged up that instead of replacing it with another de-tuned stock 323 exhaust I could use the replacement as the perfect time to upgrade to the S52 exhaust, since it has been reported that from the factory the biggest de-tune the 323 received was in terms of the exhaust. All to make the 328i and M3 of the same years appear to be more powerful, rather than keeping the 323 the way it could've been built from the factory, and make the 328i and M3 MORE powerful. Pretty lame honestly, but it is understandable from a cost of production standpoint.

At this point, I will be sourcing a good condition OEM 323 exhaust to put back on and re-test ASAP.
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Old Wed, Dec-13-2017, 12:45:31 AM   #16
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Default Re: Smog Fail. Tried previous M3F solutions... Stuck. What next?

sounds like you are on track!!!!

cats failing @ 80k miles.... not so surprising. there are a few things that can kill a cat.

GL.
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Old Wed, Dec-13-2017, 02:09:24 AM   #17
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Default Smog Fail. Tried previous M3F solutions... Stuck. What next?

Short drives it whole life…
Why not have an exhaust shop weld in a pre/post cat crossover with an O2 bung?
And talk to Turner to see IF they offer a Shark Injector for the 323 with free flow exhaust.

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Last edited by bluptgm3; Thu, Dec-14-2017 at 01:16:16 PM.
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Discussing Smog Fail. Tried previous M3F solutions... Stuck. What next? in the E36 M3 (1992-1999) Forum - {Euro - S50 B32 321hp @ 7400 rpm} {U.S. - S52 B32 240 hp @ 6000 rpm}
Total Produced: 71,212 - Years Produced: 1992 to 1999 at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)