loud knocking from the engine and it gets louder as drive. cly4 misfire

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I have loud knocking from my engine after filling up with gas from a 7 eleven. Before I put that gas in everything was fine. After filling up the next morning when I started up my car it started knocking. Then the check engine light came on indicating a misfire in cylinder 4. The knocking gets louder as I accelerate. I have checked the spark plug and cleaned the rockers and lifter tubes. It still knocks and check engine light is still reading misfire cyl 4