how come my 2004 chevy 2500HD 4x4 fuel pump dosent turn on?6-speed 6.0 v-8

2004 CHEVROLET SILVERADO
78,000 MILES
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TARGITED8745
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i was driving down th road and all of a sudden my truck died. the fuel pump dosent sound like it turns on at all. i put a new one in it and it turned on for 2 seconds and that was it, i pushed the valve stem on the fuel rail on the engine and it had no fuel or pressure.
Jan 28, 2012 at 10:01 AM
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CARADIODOC
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It should run for just two seconds. You don't want it to run with the engine off after a crash that ruptures a fuel line. Does the pump run while cranking the engine?
Jan 28, 2012 at 12:49 PM
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TARGITED8745
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no it dosent. it only turn on for 2 seconds the very first time i tryed to start it after installing the new fuel pump. is the a shut of valve or should i replace the electric relay located in the fuse box under the hood? i pulled it out and two of the contacts have a purple look to the right next to the entrance of it. not the fuse box. the relay its self. i did notice the numbers on the realy were backwards of the numbers shown on the fuse box. i think it fryd it or could it of fryed ecm?
Jan 29, 2012 at 9:40 AM
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CARADIODOC
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If the relay was bad, the pump wouldn't run for those first two seconds. A common cause of this problem is a defective crankshaft position sensor. Without its signal, the Engine Computer won't know the engine is rotating so it won't turn the fuel pump relay on during cranking. You normally won't have spark either.
Jan 29, 2012 at 2:48 PM