Sounds like you have a failing fuel pump. Many of them will fail to start up but if they do, as in when banging on the tank to jar it, they will keep on running until you stop the engine. Then, the next time they may fail to start again or they may start fine for weeks. The clue is banging on the tank got it going the first time.
You can verify this by checking for spark and fuel pressure when the engine doesn't start. If you have spark but no fuel pressure, the fuel pump is the main suspect.
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Saturday, September 21st, 2013 AT 12:15 PM