OT: E46 330xi Stock Exhaust Manifold Question

[athayer187]

So, I haven't gotten any responses over on E46Fanatics for days, and I know there are a few fellow E46 owners here.

My 2004 330xi needs new exhaust manifolds and cats. I'd like to replace them with OE BMW units, as the quality of aftermarket options looks iffy at best.

Researching options, it appears that the 325xi, 325i, and 330i all use the same exhaust manifolds/cats, but the 330xi has a different part number. Anyone know what the actual physical difference is? Another data point is that 330xi's can run aftermarket headers with no issues.

Long story short, I can get used cats off of 330i's for <$250, while new 330xi cats are <$1600...

Thanks for looking!

[mooseheadm5]

The xi manis have to clear the front axles.

[athayer187]

The xi manis have to clear the front axles.

I agree, they do.

The most puzzling fact is that everything else is the same (325xi, 325i, and 330i) while the 330xi has different P/N manifolds.

[slammin_e28]

Another data point is that 330xi's can run aftermarket headers with no issues.

Wait what?

What do you mean by no issues? It will def set a CEL.

[athayer187]

Another data point is that 330xi's can run aftermarket headers with no issues.

Wait what?

What do you mean by no issues? It will def set a CEL.

No fitment issues, sorry.

[mooseheadm5]

I'm out of ideas then.

[Lucas_Roehr]

What would make a set of after market headers set a fault?

[slammin_e28]

What would make a set of after market headers set a fault?

Cats are in the oem manifolds. You put headers, you delete cats.

I put headers on my 330i and have a CEL all the time.

[Lucas_Roehr]

HA! I've got the fix for you!! I've seen people with headers add a catalyst after the header and weld o2 bungs down stream. But even better:
[/img]

[Lucas_Roehr]

It pulls the sensor out of the direct stream so that the sensor reads steadily and in most cases does not set a DTC. I know someone with an e46 M3 with pacers built in to his headers and he never gets cataylst faults...

[ldsbeaker]

HA! I've got the fix for you!! I've seen people with headers add a catalyst after the header and weld o2 bungs down stream. But even better:
[/img]

Slick.

[Mike W.]

My understanding of OBDII and after cat O2 sensors is when the cat is working properly the pre and post cat readings don't match. If they do match it means the cat isn't doing it's job and it sets a code.

[slammin_e28]

Those won't fit with the popular Ebay headers.

[mooseheadm5]

What about these:

http://vibrantperformance.com/catalog/p ... 5f5196a003

[slammin_e28]

The one bung is right up against the body of the car. Other one is close to the frame rail. Otherwise, for $80 shipped, these headers aren't bad. Have to run two of the sensors in the wrong holes to get it to run, then the other two sensors go in a box (household electric outlet housing) in the "drug bin" to have o2 sims tapped into the harness.

I also removed my air pump as it was not necessary and there is a sim box for that as well. Euro cars have a block off plate where the air pump valve goes on the head, which I got and installed.

All in all the car sounds great. Stock exhaust with the headers. Donno about power or whatever, but it has a nice rasp to it. Since we don't have emissions here....no problemo. Nobody ever checks to see if emissions devices have been "tampered with" around here either.

But seriously, the money that cats cost, and BMWs being as picky as they are about what cats go in....I ditched them.

[Lucas_Roehr]

My understanding of OBDII and after cat O2 sensors is when the cat is working properly the pre and post cat readings don't match. If they do match it means the cat isn't doing it's job and it sets a code.

Yessir. The upstream switches constantly from rich to lean to manage fuel trim (obviously), and the downstream should just about be a steady voltage in the middle (as the catalyst should smooth out the rich/ lean surges). By spacing it off of the manifold (if I understand it correctly) the o2 sensor probe is not directly in the exhaust stream and the pocket that the probe sits in makes the o2 read somewhere in the middle of the rich/ lean surges and makes a voltage pattern similar to a working catalyst.