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2002 Taurus Wagon 3.0 OHV 91k miles. On occasion my fuel pump with run 30 to 40 seconds after ignition is turned off. Most of the time it runs normal. Meaning when switch is turned on pump starts with a smooth hum for a second or two and when ignition is shut off it shuts off. When pump does continue to run longer than normal the pump sounds rough as if it is going bad. I replaced the fuel pump relay and no change, it remains as a random event. OBD shows 40lbs +/- fuel pressure. Car runs fine with good gas mileage. I can only guess at the start up sequence. My guess, ignition on, relay activates pump, pressure sensor shuts pump on and off as required while engine running. If that is the correct sequence I would think pump could not run after ignition shut off. Any suggestions would be greatly appreciated, Thanks HRTULL
 

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2002 Taurus Wagon 3.0 OHV 91k miles. On occasion my fuel pump with run 30 to 40 seconds after ignition is turned off. Most of the time it runs normal. Meaning when switch is turned on pump starts with a smooth hum for a second or two and when ignition is shut off it shuts off. When pump does continue to run longer than normal the pump sounds rough as if it is going bad. I replaced the fuel pump relay and no change, it remains as a random event. OBD shows 40lbs +/- fuel pressure. Car runs fine with good gas mileage. I can only guess at the start up sequence. My guess, ignition on, relay activates pump, pressure sensor shuts pump on and off as required while engine running. If that is the correct sequence I would think pump could not run after ignition shut off. Any suggestions would be greatly appreciated, Thanks HRTULL
Pump module is powered by a relay and if the relay does not open, there will be power to the module. If the key is off and it is still powered up by the relay, you do not have the signal from the PCM to manage the volts for pressure management by the module. Thus you can have a over pressure. Highly like not the module at fault as it should have no power when the relay opens. The pressure is regulated by adjusting the duty cycle of the negative line to the pump motor. The positive side of the pump motor is powered by battery volts through the relay.


-chart-
 

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^ Fwiw, he said he replaced the fuel pump relay to avail...
The only source of power is through that relay and the inertia switch. I would have someone help by turning the key off while the engine is running then I would pull the relay and see if that kills the pump. If so, the source of "run on" is the signal to the relay.


-chart-
 

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Possible intermittent short to ground in the pump relay coil to PCM control circuit.
 

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Discussion Starter #7
"I would have someone help by turning the key off while the engine is running then I would pull the relay and see if that kills the pump. If so, the source of "run on" is the signal to the relay."

I assume the signal to the relay would be controlled by the PCM which is activated by the ignition switch. Wondering if ignition switch could be an issue. So I guess that somewhere , some how a signal is being generated to fuel relay, so let the hunt begin. I will try to remove relay as suggested . Am I correct in thinking pump can only be activated thru the relay, if relay removed there is no other power source . Thanks
 

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Correct..... pump is powered, via the FPDM, directly from the FP relay as shown in Charts diagram. Pump can not run with the relay out of the circuit.
 

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Also the PCM must have another criteria to keep the pump running other than the ignition switch. It must be something like the RPMs, cam pulse or a crank pulse since the pump is timed to shut off in a couple of seconds when just the ignition is turned to run position.
 
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