S54 running (slightly) rich

[Arclitgold]

I’m dealing with this exact same issue. However I have reason to believe that my cats may be also going bad.

I’m planning on getting all o2 sensors replaced, and then remeasuring the o2 voltages as it appears my Bank 2 post cat voltage is fluctuating at the same rate as my pre-cat.

[Slideways]

I’m dealing with this exact same issue. However I have reason to believe that my cats may be also going bad.

I’m planning on getting all o2 sensors replaced, and then remeasuring the o2 voltages as it appears my Bank 2 post cat voltage is fluctuating at the same rate as my pre-cat.

When the post sensor voltage follows the pre sensor voltage, that does indicate a bad cat. As long as you do not have O2 sensor codes, the sensors should be working correctly.

BMW does suggest 100k mile service interval for O2 sensors.

[BL92]

1 of post cat 02's is dead, i do not think that effects LTFT

I have a slight stumble at start up from time to time, i am thinking injectors are shot

[ATB88]

Back on the old forum pre-2020 I had some long thread about chasing lean LTFTs and seemingly less than ideal fuel economy, threw basically every part one could throw at the car, it never changed anything. I wonder to what extent LTFTs on some engines are the way they are simply due to manufacturing tolerances on the heads, valves, etc?

Car's modified and tuned now (whereas was bone stock back when I was chasing this down), so I figure it's not really meaningful to compare current LTFTs to the ones that I was trying to fix before.

I kind of wish my old thread still existed to try and dissuade anyone from getting too obsessed with fixing this. Then again, if people are able to make discoveries about how to diagnose these issues that I missed, I'm interested in seeing it happen!