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I'm looking at doing some aftermarket bits to my beast, Tubi Exhaust, GruppeM RAMAIR Induction, Chip, SPEC Stage 5 Clutch and flywheel. But i'd also like to put a CAT bypass in the exhaust. I've been warned by BMW that this can upset sensors and cause problems with the ECU. Is this true? Is there a way around it?
 

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You non-north american guys correct me if i'm wrong here, but I thought the North american market was the only ones who got the post cat o2 sensors, part of obd2. If you don't have those, taking out the cats would not cause any issues, other than needing software to correct for less restriction.
Mike
 

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mottati said:
You non-north american guys correct me if i'm wrong here, but I thought the North american market was the only ones who got the post cat o2 sensors, part of obd2. If you don't have those, taking out the cats would not cause any issues, other than needing software to correct for less restriction.
Mike
Mike you need some sort of sensor to tell the ECM how rich or lean the exhaust is in order to fire the proper injector pulse width. Whether it's a O2 sensor or a simulator.



Joe
 

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hudson said:
Mike you need some sort of sensor to tell the ECM how rich or lean the exhaust is in order to fire the proper injector pulse width. Whether it's a O2 sensor or a simulator.

Joe
Right, and that's what the pre-cat O2 sensor is for. I was under the impression that Euro spec m5's do not have the post cat O2 sensor, and in that case, taking the cats out would not make a difference. If they do have post cat o2 sensors, like we do, then yes you'd need an o2 simulator to avoid the ses light.

Didn't someone remove their cats, M5rus (someone from russia, i thought).
Mike
 

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mottati said:
Right, and that's what the pre-cat O2 sensor is for. I was under the impression that Euro spec m5's do not have the post cat O2 sensor, and in that case, taking the cats out would not make a difference. If they do have post cat o2 sensors, like we do, then yes you'd need an o2 simulator to avoid the ses light.
Sorry Mike I misunderstood the question. Your right cars built for and in North American since 1996 have an OBDII system which includes a post cat O2 sensor. It's only used as a monitor to tell the ECM how the emissions in the exhaust are doing down stream. If you disconnect it the SES light will come on. In PA our emission test would fail the car if the SES light is on at the time of inspection.

Joe
 
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