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Fuel cut off switch?

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Old Mar 31, 2014 | 11:20 AM
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Fuel cut off switch?

I am in the process off trying to troubleshoot my fuel system problem. At the cutoff switch,I unplugged the switch and I am getting about 6.5 volts on the green wire with yellow stripe. When I plug it back up, I get no power. I also jumped the switch and lost power. Is this normal? Or is a component down the line shorted? Thanks for any help?RICK
 
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Old Mar 31, 2014 | 11:39 AM
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Originally Posted by rickcaspari
I am in the process off trying to troubleshoot my fuel system problem. At the cutoff switch,I unplugged the switch and I am getting about 6.5 volts on the green wire with yellow stripe. When I plug it back up, I get no power. I also jumped the switch and lost power. Is this normal? Or is a component down the line shorted? Thanks for any help?RICK
The switch will only have voltage for a couple of seconds and not hot all the time.
 
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Old Mar 31, 2014 | 02:51 PM
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More specifically, it will only have power for about 1-2 seconds at initial power-on, then will not have power again until the PCM detects that the engine has fired.

It is only during that 1-2 second initial priming cycle that a voltage check will be valid.
 
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Old Apr 1, 2014 | 06:47 AM
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Thanks for the info. I'll have someone turn on and off the ignition to check the voltage. Should the voltage be 12v and is it feed directly from the PCM.RICK
 
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Old Apr 1, 2014 | 06:50 AM
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It is battery voltage and is NOT fed from the PCM. It goes through a fuse and a relay and the relay is turned on/off by the PCM.
 
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Old Apr 1, 2014 | 08:12 AM
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Originally Posted by rickcaspari
Thanks for the info. I'll have someone turn on and off the ignition to check the voltage. Should the voltage be 12v and is it feed directly from the PCM.RICK
Originally Posted by projectSHO89
It is battery voltage and is NOT fed from the PCM. It goes through a fuse and a relay and the relay is turned on/off by the PCM.

it depends what you are working on. older trucks used a fuse and relay to supply power to the fuel pump, after 04 i believe it was fuel pump power comes from the computer.
 
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Old Apr 2, 2014 | 08:35 AM
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The truck is a 2004 work truck with the 5.4L. I wasn't sure if the fuel pump was powered directly from the PCM thru the fuse box or if it is fed thru the safety switch or what. My main question is how the power is distributed thru this system. If anyone can explain this to me, it would be greatly appreciated.RICK
 
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