The longer my 2000 Ford Explorer (4.0 SOHC) sit with the engine off, the harder it is to start. The engine turns over but does not fire. On the second turn of the key it will start. It starts better if I turn the key to the run position for 10-20 seconds before trying to start the key. I've looked for any leaks in the fuel line with no luck. Poured a fair share of different cleaners and sea foam different tanks of gas. I have picked up a new fuel filter, but when I went to depressurize the line with the Shrader valve, I get no fuel coming out. Any thoughts?