1989 740T auto 180K miles. Engine in good shape, NGK spark plugs have a light tan insulator, a bit of black fluff on metal part of plug. Good air filter. Time to change the oil. Original injectors. Fuel Filter about 50K old- got one, plan to change it. Brather box needs changing, but no excess crankcase pressure build up.

Problem:
Car stalls when vac / boost guage hits about 11:00 position, more if the pedal is floored & the car goes into boost. Engine seems to ping (I have a hearing loss & can't hear engine noises well) & the car blows a sort of light gray smoke that does not smell oily nor gassy. The car will accelerate fien up to the point, and then it acts like a fouling plug, and will major bog down if I floor it.

Does anyone have any ideas? My first guess, after the Fuel Filiter, is the cat, but I am trying to avoid guess and replace.

Thanks in advance.