If your speaking of valve problems on the V8s I would assume you are speaking of the Active Fuel Management (AFM) system on some of the LS engines. AFM, when operating normally, works very well and is great for consistent hwy fuel mileage. However if not maintained it will malfunction. To keep this system up to tasks 3k oil changes are critical, you can't let the oil get dirty. Use only 5w30 conventional.
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