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Discussion Starter #1 (Edited)
Sorry about the alliteration in the subject line..

Does anyone have definitive specifications on how to space O2 sensors to avoid CEL on catless systems on the E39? I might be going catless to avoid sinking a ton of money into cat replacement (mine are cooked).

So far, I've noticed the two configurations:
- Two spacers (1/2") and a hole to 3/8" (one report said perfect, another gets a CEL at 140mi)
- One thick spacer (1/2") and a hole to 1/2" (one report)

I am aware of how fussy BMW O2 sensors are. Anyone have a definitive answer on this one? Is it even possible given the S62's wide range of operating conditions?
 

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Before you go catless, consider talking to Clemster about used cats from his fleet of donor vehicles.
 
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Discussion Starter #3 (Edited)
Car's already at the exhaust shop, and we're pulling the trigger on catless if it isn't idiotically loud. I don't have e-tests where I live. So the question is really about what the magic combination is for O2 spacers. Well that plus I'm in Canada, plus ..etc but thanks for the suggestion.
 

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The general consensus is spacers can work to cure the B2 and B3 code but not to go catless. Also no two cars seem to be the same. You must adjust them to make work on your car. If they work for B2 and B3 you should be able to make them work catless.
What province? Almost all provinces have enviro cops and it is easy to get caught because of the smell. Ontario and Quebec are the worst for getting busted, and the fine will shock you. Not sure you will be able to tolerate the smell yourself.
Anyway longer spacers with two chambers seem to do the trick, I played with them a lot. I would use spark plug anti fowlers. It takes two per side one has to be cut short to get the whole length to fit. The cut one goes in the exhaust then the other screws into it, then the sensor. You have to have it all together to get it in.
For no cats you may need to experiment, but I would start with a larger hole in the one that is in the pipe to get flow then slightly smaller hole in the top one. The two chamber design gives better simulation of readings. All that said you need to have a tool so you can watch what the readings when you make adjustments.
 

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Discussion Starter #5
The general consensus is spacers can work to cure the B2 and B3 code but not to go catless. Also no two cars seem to be the same. You must adjust them to make work on your car. If they work for B2 and B3 you should be able to make them work catless.
What province? Almost all provinces have enviro cops and it is easy to get caught because of the smell. Ontario and Quebec are the worst for getting busted, and the fine will shock you. Not sure you will be able to tolerate the smell yourself.
Anyway longer spacers with two chambers seem to do the trick, I played with them a lot. I would use spark plug anti fowlers. It takes two per side one has to be cut short to get the whole length to fit. The cut one goes in the exhaust then the other screws into it, then the sensor. You have to have it all together to get it in.
For no cats you may need to experiment, but I would start with a larger hole in the one that is in the pipe to get flow then slightly smaller hole in the top one. The two chamber design gives better simulation of readings. All that said you need to have a tool so you can watch what the readings when you make adjustments.
Thank for this. In the end I just replaced the cats with high flow cats. We fired it up with just the resonator and it was WAY too loud. Like almost insane. I'm not going to say I didn't like it, but I also don't want to wake up the neighbourhood on my way to work.

Anyway, thanks for the concise post, I am sure it will be useful to others. I have gone catless on my other M cars including my E36 with Stg1 supercharger. I quite liked the smell.. it's a manly smell of horsepower.
 

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The general consensus is spacers can work to cure the B2 and B3 code but not to go catless. Also no two cars seem to be the same. You must adjust them to make work on your car. If they work for B2 and B3 you should be able to make them work catless.
What province? Almost all provinces have enviro cops and it is easy to get caught because of the smell. Ontario and Quebec are the worst for getting busted, and the fine will shock you. Not sure you will be able to tolerate the smell yourself.
Anyway longer spacers with two chambers seem to do the trick, I played with them a lot. I would use spark plug anti fowlers. It takes two per side one has to be cut short to get the whole length to fit. The cut one goes in the exhaust then the other screws into it, then the sensor. You have to have it all together to get it in.
For no cats you may need to experiment, but I would start with a larger hole in the one that is in the pipe to get flow then slightly smaller hole in the top one. The two chamber design gives better simulation of readings. All that said you need to have a tool so you can watch what the readings when you make adjustments.
Do you think it would work on BMW M6 e63? I mean the spacers from CEL perspective (with OEM cats)
 

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Yes it would work but hitting the right length and the right size of hole is done with experiment. I have no idea if you have the space or what might be required. There are spacers that turn the O2 sensor 90 and have mini cats in them, they are not cheap but work well on first install.
 

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