Car won't start for 4 hours after use

Hello,

I have a 2001 Lincoln Navigator that will start and run fine at first however, after turning the engine off after having driven for 30 or more minutes, it won't turn on. The engine will start, however won't turn on. If I wait for 4 hours or more, the car will then again start & run just fine.

There is no check engine light. When I put starter fluid into the air intake while turning the key, the engine will start but not continue to run. It seems like gas is not coming into the engine. I have replaced the Fuel Pump Relay but the problem persists. I believe it may have something to do with the car needing time to cool down. Any help would be greatly appreciated.