[Joshua33]

Good day people,

So a few weeks back I went to a quite popular indie exhaust shop where I live to install catless downpipes.

It's quite expensive to buy and ship aftermarket downpipes where I live at the moment and I wanted a temporary cheap downpipe to install.

They had a cheap ebay one on shelf but the guy there had a different suggestion and said he did it for countless N55 folks and worked just fine but never for N54s. I still went with it.

He took off the stock downpipes, cut off the catalytic coverters with a dremel and welded 2.5" piping in their place keeping both ends of the downpipes stock. I was standing there inspecting the whole process so I'm sure the welding was perfectly done but of course the piping is not exactly the same as the cats pipe cus the cats were pretty straight and larger in diameter.

He plugged the O2 sensors back in their place (stock part of the downpipe) and put it all back in.

I'm currently running FBO running MHD stage 2 and xHP stage 3. Car runs great no power loss especially when it comes to going WOT.

Problem is, it threw a 2c9c code (Oxygen sensor heater before catalytic converter: Activation) when inspected and comes back immediately if cleared.
Car runs a little rough when going slow i.e. less than 25% throttle and has a rough idle (idles at ~850 rpm instead pf the normal 600rpm).

Sometimes it idles at 600 normally and seemingly acts normal and sometimes it becomes a little too rough.

It also threw 29E1 and 2A2C (Mixture Control 2) but my understanding is that those are related to that O2 sensor not activating.

My mechanic inspected the O2 installation and said it looked fine. Even installed a spare O2 sensor he had that was working just fine on another 335i to no avail.

Any ideas? Should I install O2 sensor spacers or what should I do?

Any suggestions or help would be greatly appreciated.
Sorry for the long post and have a nice day folks.

[type-dRew]

Its a heater code, you need new primary sensors.

Easy to damage the heaters while removing and installing, always smart to do new sensors when installing because they are considered wear items anyway.

[dpaul]

What is curious is that your sensor heater code is on bank 1 but your mixture control codes are on bank 2.

You've got more than one problem.

Which bank did your mechanic install the used sensor on? Did that change anything at all? Did you clear the codes before re-testing?

[Joshua33]

Originally Posted by dpaul

What is curious is that your sensor heater code is on bank 1 but your mixture control codes are on bank 2.

You've got more than one problem.

Which bank did your mechanic install the used sensor on? Did that change anything at all? Did you clear the codes before re-testing?

I looked into photos of aftermarket catless downpipes and compared it to the one the shop retro made/fitted for me and I think I found the culprit and will be visiting the shop asap to correct what could be the problem.

There is some sort of nut or spacer on the holes where the O2 sensors plug that were not made on my current catless downpipes. It keeps the O2 sensors from being too far into the pipe. I suspect that could be why they are getting a faulty reading and my mechanic told me he unplugged Bank 1 O2 sensor temporarily since I told him I don't use the car currently and is parked until I find a solution for this. He said the car runs very poorly with bank 1 connected so he had to do that so I could at least drive home and park it there.

I hope this spacer would be my issue cus there is an obvious difference between how far the O2 sensors are plugged atm and how they are on aftermarket downpipes. I don't have photos of them curre tly but my mechanic is the one who confirmed they didn't have those nuts when he took the O2 sensor off to replace it thinking it's faulty.

Thanks in advance.

[dpaul]

What in the world are you talking about?

In your first post you indicated that your mechanic cut the cats out of the original downpipes and replaced that portion. Thus, you've retained the original O2 ports. If so, they will function normally. What an aftermarket pipe might look like (especially one of unknown manufacture) is completely irrelevant.

Sounds to me like it might be time to visit a new mechanic

[langsbr]

I would get a new mechanic and get a set of legit catless downpipes.

Id wager your mechanic 'offered' this service knowing he could sell your cats for good money.

[Joshua33]

Originally Posted by dpaul

What in the world are you talking about?

In your first post you indicated that your mechanic cut the cats out of the original downpipes and replaced that portion. Thus, you've retained the original O2 ports. If so, they will function normally. What an aftermarket pipe might look like (especially one of unknown manufacture) is completely irrelevant.

Sounds to me like it might be time to visit a new mechanic

My bad, I should have corrected that part in my original post but I completely forgot. I used to think the O2 sensors plugged into the stock portion but they don't. They plug into the catalytic converter portion that is now catless i.e. they're plugged into the brand new portion that the shop made and welded. And the space between the O2 sensor and the new hole doesn't seem to be up to the oem specifications, hence the wrong readings and messed up AFR.
Also, it was not my mechanic that cut and welded the downpipes, it was another independent shop. And I even took the car to another service center and they agreed that the issue could be what I suspect was done wrong in the new catless part.

I just wanted to hear opinions in addition to what those people think before I sent my car to get this fixed (free of charge anyway as it's their fault). Thanks anyhow much appreciated!

[Joshua33]

Originally Posted by langsbr

I would get a new mechanic and get a set of legit catless downpipes.

Id wager your mechanic 'offered' this service knowing he could sell your cats for good money.

I've got my cats sitting somewhere in my garage at the moment so that's not the case.
This job cost my roughly $80 and is meant to be temporary till I can order and receive legit catless downpipes which would cost somewhere in the ballpark of $850 after adding shipping and import costs. Those are not even the pricey ones, I'm looking forward to get the VRSF catless downpipes. Cheers!