Dealing with Headers, Cats, O2 sensors, and Emissions

I've searched through here but have found a whole lot of dead ends and threads that lead to unproven theories.

Can somebody give me info on the possibility of running headers, aftermarket cats, and still meeting emissions standards. I'm considering throwing headers on the green machine but want to do so in a fashion that still give me the ability to pass emissions legally.

I've heard about O2 sensors but it seems like that won't work. So what about the possibility of running atermarket headers, magnaflow universal cats, and a custom tune... or is that another dead end?

If you weld in some cats after the headers and relocate the post cat sensors to well, after the new cats, why wouldn't it work?

If you have quality aftermarket cats installed and the O2s in the proper positions you should be able to pass with the O2s relocated but not 100% sure. I think the EU2 factory flash should take care of any software issues if you still get codes.

For what its worth, my previous e46 with headers (I did not own it at this time) did not pass visual in NC with magnaflow race cats and rear O2s relocated with no codes. The tech said it was not legal to relocate cats from their factory position and added this to the DMV system so the car had to be swapped back to stock exhaust to pass. So it may depend on who looks at it even if there are no lights.

I would also suggest it is worth the extra money to get metallic core cats, the ceramic ones are cheaper but very sensitive to any impact (a concern if lowered) and my prior car blew the honeycomb material out of both ceramic core magnaflow cats after about a year.

Chase,

You left out one BIG this that will be an issue! Force Induction...

-Anthony

I didnt pass inspection in Va cause i had aftermarket headers and straight pipe exhaust. Didnt pass cause he couldnt see any cats. Had a friend cut and weld in aftermarket cats and had it reinspected. Passed even tho i had CEL on. But it all depends on who is inspecting your car

In Maryland, they've always been pretty loose... They plug into your obd2 and if it doesn't throw codes, you're good to go... The issue is that "codes" include CEL and emissions linked "not ready" codes that can't be "fixed" with a obd2 scanner

With headers and a cat installed after the merge you should have no trouble passing in maryland. The car won't throw a code with that setup and MD only cares if the OBD-II system is reporting correctly.

Originally Posted by SoloII///M

With headers and a cat installed after the merge you should have no trouble passing in maryland. The car won't throw a code with that setup and MD only cares if the OBD-II system is reporting correctly.

Right but doesn't the OBD-II also provide the "ready" or "not ready" faults? Or is that only in other states?

If passing visual isnt an issue, then you should be fine with headers and aftermarket cats provided your rear o2 sensors are moved downstream of the cats. Even with stock software you should get OBD2 "ready" state for your o2 monitors with quality cats installed.

Swapping to headers is very much worth the headache on these cars, made a nice difference on my prior 2.5L, I would think the 2.8 should benefit even more.

Originally Posted by BMW2k3

If passing visual isnt an issue, then you should be fine with headers and aftermarket cats provided your rear o2 sensors are moved downstream of the cats. Even with stock software you should get OBD2 "ready" state for your o2 monitors with quality cats installed.

Swapping to headers is very much worth the headache on these cars, made a nice difference on my prior 2.5L, I would think the 2.8 should benefit even more.

Yeah I'm trying to decide how to handle this install as I'll be running FI and want to get the most out of it but in a safe fashion that isn't violating laws left and right.

- Leave on factory headers/cats : lose power but seemingly would stay legal. Likely burn out the cat quickly from extra heat
- Install performance headers with no cats : gain power but will not be street legal.. nice thing is md only does emissions once ever other year so I'd have a two year window if i passed and then did the install
- Install performance headers, universal cats, and o2 sensor : seemingly would be best of all worlds but will be costly for custom welding

Last question is around the tune... is the AA factory tune ok with the above... perhaps runs better with one than the other?

If you can afford FI, you can afford 100 bucks at a muffler shop having a car and o2 bungs welded in... Come on.

Originally Posted by 2000_328CI

Yeah I'm trying to decide how to handle this install as I'll be running FI and want to get the most out of it but in a safe fashion that isn't violating laws left and right.

- Leave on factory headers/cats : lose power but seemingly would stay legal. Likely burn out the cat quickly from extra heat
- Install performance headers with no cats : gain power but will not be street legal.. nice thing is md only does emissions once ever other year so I'd have a two year window if i passed and then did the install
- Install performance headers, universal cats, and o2 sensor : seemingly would be best of all worlds but will be costly for custom welding

Last question is around the tune... is the AA factory tune ok with the above... perhaps runs better with one than the other?

AA Stage2 tune is design to run with the Post o2 turned off. As it will impact the performance of the Tune if the Post o2 is on and getting the wrong reading...

-Anthony

Can you explain how the post-O2 sensor affects the tune please?

Do what i did, ebay heders, save the oem cats, emission time comes, put them back on! Takes about 3hours tops! Deal with the cel on

I have headers and aftermsrket cats and pass emission every year. No cat efficiency errors.

For ms43 and higher, the post cats do affect fuel trim. Ms42 is only for emission. Ms43 makes minor adjustments to fuel trim for post cats (keyword minor)

sent from my HTC EVO+ using Bimmer App

seeing how there are 2 types of FI, which one are you going for...If you are going the Turbo route, then forget the feaders...you will be installing a turbo exhaust manifold and down pipes to your exhaust....if SC, then yes, get the headers....You can flash the EU2 DME setting that doesn't have the post O2 (which means don't worry about them, just ditch em)...if you have to pass visual cat inspection, then everyone on here has told you how to accomplish that...

Magnaflow headers with cats. Easiest way, they are like oem with better flow. The price is steep but you should not have any problems at all with emissions and you'll be completely legal. However superchargers don't get along with them, they cause the cats to overheat or something. (dont really remeber the exact problem)
Goodluck