First you need to locate the leak. A small leak is only about .020" in size, so you need special EVAP testing tools to find it. I do Emissions Diagnosis and Repair work in California at a Gold Shield Emissions Station, which means that the State sends us the really hard to repair Emissions issues.
Ford Explorers have several places where they leak, the Fuel Filler Neck, the Canister Vent Valve, Vapor Control Valve and even the Fuel Cap.
Take your Ford to a shop that knows what all of these terms mean.
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