Lean faults and oxygen sensor readings, but suspect bad cats... 2.5 2004 BMW X3

I had a 2004 BMW X3 on my rack yesterday that had a huge loss of power at wide open throttle, what seemed like spark knock, a whistling exhaust (but may have been engine) and really high RPMs, and had a misfire on cylinder 3 along with lean running faults all set at around 2500-3000 RPM. My FTs each on both banks totaled around 12-14%, however my STFTs stayed close to 0 at WOT. My oxygen sensor readings at WOT were pegged lean(weird because my STFT is not showing a correction), and I am widely suspecting bad catalytic converters (pretty common on this 2.5 motor). However, in your book you mention that at WOT my oxygen sensors may read rich, and a lean condition at WOT could be fuel related. I did not get approval to dig into whether the exhaust had too much back pressure or to see fuel pressures as the customer took the car and went to the dealer to buy a new one. But my question is I have a strong suspicion this car needed cats, but my oxygen sensors are contradicting that thought. Can you help me out with this one? The engine is MAF controlled, does a rich condition show on a MAP engine because it is seeing a loss in pressure in the intake manifold and MAF does the opposite? Can somebody help me out with my diagnostic process and where I may be wrong?

Also to note, before all these readings I fixed the initial issues when I did a smoke check and found one vacuum leak that I fixed with a new OEM rubber plug that goes on the back of the manifold, smoked checked again and passed O.K., and replaced one faulty ignition coil. The ignition system on this car could have used a good refresh, but again the customer was cheap. This may be an open ended question as I do not have any other diagnostic data to provide you, but am curious on your thoughts at face value.

Thank you for being an awesome teacher btw, I have gotten one other guy in our shop hooked on your stuff. Hes pretty smart and has a lot of potential and I'm very proud of him.

Do you happen to have any captures or screenshots of your test drive? They're not required, just helpful. Do you recall what the codes were? I'll throw in my two cents because, well, the car is gone and we'll never know if I'm wrong! :silly:

IMO, without seeing more data, it sure sounds like there was a lack of fuel to me. On MAF engines, a plugged cat almost always results in a rich upstream sensor on the bank with the plugged cat. Lean on the bank without the plugged cat, if it's a V-engine or in-line with more than one bank.

My understanding is that a MAF engine with a plugged cat will still show rich at WOT because the MAF is still doing its job correctly, despite the breathing problem. In other words, if the engine was breathing 30% less air, the engine controller is still going to add the proportional amount of fuel to the measured air mass. Did that make sense?

You noted pegged lean upstream sensors at WOT and lean fault codes, which is good enough for me to suspect a fuel delivery problem. The spark knock goes along with that, due to the lean condition. Your short term trims won't adjust at WOT because there's likely an Open Loop strategy at work during WOT or heavy loads.