BMW Repair: Malfunction BMW 3 serie, combustion chamber, carbon buildup

Question
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Followup To
Question -
Micheal,
Thank you again for your time.
So as I said am ggoing to keep you informed.
Well, they finally ( yesterday) told me they have found
the problem. Valves 3 and 4 burnt.
I ask how come and they say it's because of our "bad fuel". I have great problem accepting it 'cause all my
cars were EFI and never burned any valve using the same "bad fuel". I told them to show me one BMW which have had the same problem because of using the same
fuel all cars ( inclusive all BMW-s) uses on the Island.I think that the valves burnt in proces of trying to clean them up chemacally. They through out my katalyst thinking and saying that it was the cause. Do I have to pay for all this?. Just want to inform myself before starting discussion/negotiating with them.
Thanks

Answer
The quality of the fuel has nothing to do with burning valves, any impurities that would cause such a thing would first clog the injectors, valves get burned because of carbon buildup or oil entering the combustion chamber, the katalyst being clogged implies that the mixture was rich or the car was used only for short trips and never had the opportunity to burn off deposits.  I can not fathom how a group of people would accept shitty fuel as their only option and buy a new car every 50,000 miles, then again people on the mainland do buy disposable American cars.
-cheers