Originally Posted by
oldford
A blocked cat or pre-cat could explain the loss of power.
It does not explain why the mixture is so lean.
A extreme lean condition on the other hand could destroy the cat or pre-cat.
So even with a blocked cat or pre-cat you need to investigate further.
I have looked at a car the same model with the same fault recently, when warm it held back losing power on WOT, the hotter it got the worse it was. When pulled over and got customer to rev car stationary it sounded just like a blocked exhaust, hissing sound and hot gases. Another garage had fitted a new cat and EGR valve.
I disconnected the exhaust both before and after the cat but the fault was still there, this led me to check fuel pressure with a gauge in-line to the feed to the fuel rail and when faulting the fuel pressure dropped to 1bar on acceleration. Strangely this car had no lean mixture fault codes at all.