Hmm. Interesting. Running open loop (o2 disconnected) will generally richen the mixture.
The reason I asked if the head was ever rebuilt is because they can shave the head and that can slightly raise the compression leading to ping.
Checking the FP can't hurt if you can do it easily.
My guess is the same as Jeff's - carbon. Ever heard of an Italian Tune Up?
Bellevue WA
90 535iM - not much stock remains. 3.7 liters, ported head, cammed, 3.73 diffy, M5 brakes, MAFed, yadda yadda yadda
86 Porsche 951 - Track Toy
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