Saab Repair: Fuel Mix Issue?, air flow meter, faulty readings

Question
I have a 2000 9-3 Conv. with the 2.0L turbo. At 54,000 miles the no.1 piston shed a piece 1/2" X 3" parts of which took out the Turbo. I purchased a short block from Saab and had to get a remanufactured Head and a new Turbo. Everyone I spoke to during this rebuild thought it was a preignition knock issue even thought we ran Premium. We NEVER could hear it knock. The car ran great for 2500 miles after it was completed then blew the same amount off the new No.1 piston again. I had the injectors spec.'d and they are perfect. Where do I look next as I can't afford the time or money to rebuild this car every 2500 miles. I was told by the head shop to ceramic coat the piston tops which I am willing to do but clearly they are getting too hot. This time when the chunk came off it vaporized into aluminum powder.

Answer
Replace the air flow meter. The most likely problem is faulty readings from the air flow meter causing a super lean condition. we have seen this exact problem a couple times, thogh we've never burned up a second engine. If you have a tech 2 you can ck the read values for a lean fuel trim condition.