[kacpere90]

Hello,

So recently I've decided to replace both catalytic converters on my E90 325i. One of them was completely burned out. I've replaced them for used originals, which I checked before installing with endoscope (both were full and I didn't noticed any cloggage). It turned out that I also had to replace three o2 sensors (both post-cat and bank 2 pre-cat).

After few weeks I started getting errors: 29F5, 29F4 so poor performance of catalytic converters. They appear once every few days/week and I think that I've noticed pattern that they appear after/while driving in heavy traffic, but that's not always true.

Today I've decided to log o2 sensor voltages, but I'm unable to tell if and what is wrong, so I put a chart below. One thing I've noticed that one of post-cat sensor is quite noisy compared to second one.

What would you suggest as further diagnosis?

(voltage over time)

[Bims328i]

I would love to learn more about this as I get a reoccurring 29F5 code. Specifically, the bank 2 cat (rear set). I have used replacements but have yet to install them. Still trying to figure this issue out. After doing my pan gasket for whatever reason, the code doesn't pop up quite as often.

[VehementCrom]

I get those but it’s because I have a header and no cats. Are the cats hollowed out or removed?

[kacpere90]

Originally Posted by VehementCrom

Are the cats hollowed out or removed?

As I stated, I've recently replaced both of them (one was completely hollow, probably burned out). I've inspected new ones and they were full and quite clean inside.

I think that I've noticed a slight choking while starting from the stop, because I remember that right after changing the cats it ran smoothly when starting slowly.

[kacpere90]

Bims328i Since posting about that problem I've done few repairs and now (for like a month) the error is gone. Two major things I've done were replacement of Vanos cam gear (outlet one was leaky) and oil separator replacement (it also was leaking like crazy).

I believe that the oil separator did a thing as it causes the oil to burn in the chamber and thus o2 sensor get wrong info about mixture