02 sensor question on headers-question for any m54

[lo_jack]

I have my headers mocked up, sitting on a couple of studs on the head. I have been reading a lot, and it seems like the e46 people put on headers, stick the fueling 02 sensors in the first available set of bungs in the collector and then disregard emissions. They end up hit or miss on check engine lights and their cars probably smell horrible if you sit behind them.

That seems silly.

One of the reasons I think this happens (besides not using cats, which is asinine) is that the 02 sensors in all E53/e46 era manifolds--the sensors that control fueling--are right off the head. No cheap header design replicates that, instead putting the fueling 02 sensor down at the collector. I believe this negatively impacts fueling and the ECU's expectation of data from the head.

So the question is, has anyone either A) not had issues with CEL/running badly with 02 sensors in the collector or B) welded a bung into the header 2" off the head, just like OEM to see if that would work better? I have half a dozen bungs and am in a place where I could mark up the headers and MIG in bungs for the upstream 02s really easily, and I might do that regardless of feedback.I am putting in good cats because ground level, smog-forming emissions and half-burned gasoline are carcinogens, and I like breathing.

[e39_touring]

I run headers and just the upstream sensors, and the car runs great. I'm not running cats and have picked up about 3 mpg on the highway to about 24 going 65-70.

You definitely want the o2 sensor at the collector, or you'll only be reading 1 cylinder's mixture. You can run cats and choose whether or not to program out the downstream sensors. The eu tune doesn't use them, and they're mostly used for diagnostics of the cats rather than refining the mixture.

[lo_jack]

That makes sense. If there was enough space I'd put the cats right off the collector. I have a bad feeling that moving the cats downstream of the head at all makes the DME freak out about cat efficiency, but I'm going to run some anyway and see what happens.

[e39_touring]

I don't have 1st-hand experience, but I did research this when doing mine. I think the issue you're going to face is in the warm-up. That's why the cats are so close to the head on the X5 - the ULEV emissions and ultra-fast warm-up. I only drive about 1.5 miles to work 2-3 days/wk, so I hardly warm-up and didn't go through the trouble incorporating cats.

What I found in my research pertains to others installing the schmeidman (sp?) setup on E39. That has headers and a mid-pipe that incorporates cats, replacing the center resonator. People installing this setup were getting codes, even with o2 sensors extended and hooked up properly. I don't recall the specific codes, but I suspect it is cat efficiency during the warm-up cycle.

I don't know if you can extend the warm-up cycle tolerance in the tune (haven't done custom tune stuff yet), but there's certainly nothing stopping you from running cats and just tuning out the downstream sensors. This is how fuel-injected cars all ran prior to the odbii standard.

[crystalworks]

I would think if you put them at the collector you would be fine as long as you don't have any vacuum leaks or other issues that would affect fuel mixtures. I also don't understand not running cats. Resonators or mufflers I can see deleting, but not cats. The couple cars I've done long tubes on did not mind... Granted neither was an m54 and one of them was OBD1.