If your drain back valve isn't working, fuel will drain back into the fuel tank and you won't have any fuel up at the engine. Then, the fuel pump has to pump fuel back through the fuel lines when you go to start the engine, which means it takes a bit to start.
On the fuel rail, there is a valve like you would find on your tires (schrader valve). Let the Jeep sit for a while then use the valve to see if there is any fuel in the fuel rail. If fuel comes out of the valve, then you have fuel at the engine. If no fuel comes out, then you don't have any fuel at the engine. If you don't have any fuel at the engine, then it has drained back into the tank and your anti drain back valve isn't working. This is probably the easiest way to test if your anti-drain back valve is not working.
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