Problem in unity, my faces disappear when i exporting my truck object or another from blender to unity some my faces disappear in unity. I add some images for better understanding.

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Select all the offending mesh in edit mode and in Shading tab select Normals: "Flip Direction". Your model appears to be facing the wrong way, so when backface culling comes into play you can only see the inside. I hihgly recommend you press N in 3D view and enable Shading: Backface Culling.