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Fuel pump running constant HELP

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Old Jul 10, 2014 | 10:15 PM
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Default Fuel pump running constant HELP
Can anyone explain to me why the fuel pump output wire from the pcm puts out a constant 12v when the key is tuned on? It does not run for a few seconds and shut off. I am using a 02 truck computer and harness. Any help is appreciated.
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Old Jul 10, 2014 | 10:48 PM
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Are you running anything else off the pcm fuel pump wire? I had a scavenge oil pump relay wired in parallel with my fuel pump relay because I wanted it to run any time the fuel pump was running and this caused the fuel pump to not turn off. I had both relay grounds going to the same place at first but when I moved the ground wire for the scavenge oil pump to a different location on the chassis everything worked fine.
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Old Jul 11, 2014 | 07:19 AM
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I do have the ecm, fan, and fuel pump relay on the same ground. Ill try that this afternoon. I unhooked the signal wire from the relay to get the pump to shut off and stuck my test light in the connector on the green wire and turned the key on. The light on the test light stayed on the whole time the key was on.
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Old Jul 11, 2014 | 07:57 AM
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Ive never seen this happen, but it sounds like the driver in the PCM is shorted to power or something.
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Old Jul 11, 2014 | 08:05 AM
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Its strange. It was working like it was supposed to in te last car.
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Old Jul 11, 2014 | 08:06 AM
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You have the fan and fuel pump relay on the same ground? If I recall one uses a ground trigger and the other is a positive trigger so they shouldn't be wired the same.
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Old Jul 11, 2014 | 08:08 AM
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I think they are. Ill have to double check and see when I get home. The relays are not wired the same but the grounds from both relays go to the same grounding point. The fan works like it should.
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Old Jul 11, 2014 | 06:04 PM
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Ok something strange. I got home and started checking the wiring. I heard a noise from the throttle body with the key on (dbw set up). So I thought it may be from the gas pedal being unplugged. I plugged it in and the fuel pump shut off. So I cycled the key a few times and all seems to be ok. I don't know why but that fixed it lol.
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Old Jul 11, 2014 | 09:52 PM
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Does unplugged gas pedal indicate WOT to the PCM somehow?
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Old Jul 11, 2014 | 10:47 PM
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Im not sure. I got the OBD2 port wired up tonight so I may check that tomorrow.
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