[Ocharlas]

SCROLL TO LAST PARAGRAPH TO GET STRAIGHT TO THE CHASE, OR PERUSE AT YOUR LEISURE.

Ok so, I won't go into the whooole story, for which I would need a publishing deal, but suffice it to say that in the 9 months I have owned this car I have had to do more work on it than all cars I have ever owned, combined. And motorcycles. And lawnmowers. And guitar amps.

After a long and hard fought battle with 30FF/constant limp mode and a myriad of other things, I removed, had rebuilt, and replaced the turbos myself (ironically it turned out to be false diagnosis by local BMW shop, wound up being HPFP. Hooray).

Upon removing the downpipes, I noticed that one of the cats was completely crumbled and shot, so I essentially gutted it and put it back on. Seeing as how it was most likely 3am and I was probably delirious, the thought to do the same to the other cat didn't even cross my mind. Now the car is back together with about 800 miles on it, and I'm getting paranoid about what I might be doing to it. I just bought the MHD monitoring software, as well as the flasher (to do the wastegate rattle fix, haven't decided if I'm going to try stage 1 yet).

When I did my first log, I noticed the STFTs were quite different. I barely know/understand what that means, but I read it has to do with 02 sensors.

So to wrap up: What is happening in my car with only one cat? Am I damaging something? Disastrous? Minor? Somewhere in the middle? What is my best course of action? Gut the other one and do MHD tune? At this point I'd really like to not have to replace the gutted one to the tune of $1200 or however much they are. But the car, though feeling exponentially better and smoother (and less limpy) than it did before the rebuild/HPFP, does still feel quite sluggish.

[BeastMode335i]

Originally Posted by Ocharlas

SCROLL TO LAST PARAGRAPH TO GET STRAIGHT TO THE CHASE, OR PERUSE AT YOUR LEISURE.

Ok so, I won't go into the whooole story, for which I would need a publishing deal, but suffice it to say that in the 9 months I have owned this car I have had to do more work on it than all cars I have ever owned, combined. And motorcycles. And lawnmowers. And guitar amps.

After a long and hard fought battle with 30FF/constant limp mode and a myriad of other things, I removed, had rebuilt, and replaced the turbos myself (ironically it turned out to be false diagnosis by local BMW shop, wound up being HPFP. Hooray).

Upon removing the downpipes, I noticed that one of the cats was completely crumbled and shot, so I essentially gutted it and put it back on. Seeing as how it was most likely 3am and I was probably delirious, the thought to do the same to the other cat didn't even cross my mind. Now the car is back together with about 800 miles on it, and I'm getting paranoid about what I might be doing to it. I just bought the MHD monitoring software, as well as the flasher (to do the wastegate rattle fix, haven't decided if I'm going to try stage 1 yet).

When I did my first log, I noticed the STFTs were quite different. I barely know/understand what that means, but I read it has to do with 02 sensors.

So to wrap up: What is happening in my car with only one cat? Am I damaging something? Disastrous? Minor? Somewhere in the middle? What is my best course of action? Gut the other one and do MHD tune? At this point I'd really like to not have to replace the gutted one to the tune of $1200 or however much they are. But the car, though feeling exponentially better and smoother (and less limpy) than it did before the rebuild/HPFP, does still feel quite sluggish.

Why not just drop $300 on catless downpipes and call it a day?

To answer your question though, any restriction in the exhaust system will create back-pressure on your turbos most likely, depending on how bad it is.. I'd suggest just getting a set of DP's though since you've already familiarized yourself with them..

[dyezak]

Originally Posted by BeastMode335i

Why not just drop $300 on catless downpipes and call it a day?

To answer your question though, any restriction in the exhaust system will create back-pressure on your turbos most likely, depending on how bad it is.. I'd suggest just getting a set of DP's though since you've already familiarized yourself with them..

He's right you know.

[Ocharlas]

That's a good option too, and probably a more realistic one too. I remember looking in the other side and thinking that that cat was much more difficult to get to.

But still the main question for me is how having one with and one without catalytic element (albeit temporarily) will affect things. It's definitely getting taken care of, but I'd love whether I need to make the time in the next day or two, or it's not a big deal can wait a little while.

[Ocharlas]

Originally Posted by dyezak

He's right you know.

About the pipes or back pressure or both? Will the back pressure cause damage to the turbos? I only ask because it seems like physically each scenario is normal...cat or cat-less - but it's obviously the fact that I'm rocking one of each that's out of the ordinary. I figured something like toasted 02 sensors, or maybe the engine management trying to compensate for something?

[Pavement Molestor]

either gut out both cats (not a good idea to have only one gutted) or just get downpipes. dont forget an ECU tune.

what is your mileage?

[Ocharlas]

Just about to hit 110k

[shadow191]

You're not likely to do long term damage by just driving around, but why not just fix it? Either gut the other one or buy catless downpipes. I would personally buy the new downpipes since you're having to remove OEM anyways. The fuel trim between bank 1 and 2 are going to be way off because the O2s are giving different readings. One bank now looks like the cat failed since it's not there. It may be sluggish because of the fuel trim difference; fix it and see.

[Ocharlas]

Cool, that's what I was hoping. I don't plan on driving around on it *much, but I probably can't get to it until next week and I put on about 6-700 miles per week for work. I really hope this gets the car running properly, otherwise I'm quite out of ideas!