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Fuel rail pressure sensor question

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Old 05-07-2015, 05:47 PM   #1
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Default Fuel rail pressure sensor question

Should the idle change at all when you unplug the fuel rail pressure sensor? '04 FX4 5.4 Been chasing a rough idle for some time now and a strange starting problem when warmed up. Truck either starts immediately almost with no initial cranking of engine, very strange and hard to explain, just starts without a noticable crank or cranks longer than usual but still starts. Im just poking around at this point and noticed there was no idle change when I unplugged the fuel rail connector. Just wanted to know if it was normal
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Old 05-08-2015, 04:56 AM   #2
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Eventually, the engine should stumble and stall. That sensor is used to inform the PCM/ECU that pressure at the fuel rails is there, which in turn is used to inform the FPRM (fuel pressure regulator module; the one by the spare tire that has been known to fail due to corrosion) to turn on/off the fuel pump in the fuel tank.
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Old 05-08-2015, 06:29 AM   #3
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Have you changed the plugs and/or Coil packs ?
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Old 05-08-2015, 07:36 AM   #4
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The warmed engine "immediate start" or "takes longer to start" has me thinking that the PCM/ECU is not getting the correct engine temp reading. On a detected cold engine, the fuel to air mixture is set higher (fuel) to get a cold engine to start, simular to the days of a choke; the choke would cut off air, and allow the fuel mix to be greater.

Once the engine reaches a certain temp, the fuel mixture is lowered, allowing the engine to return to a normal set idle.

Usually an engine today has two temp devices: a temperature sender, used by the cluster temp guage, and a temperature sensor, used by the PCM/ECU to aid in the adjustment of the fuel to air mapping.

My Ford Ranger had this setup, but not sure if these 4.2/4.6/5.4 engines have two temp devices. Perhaps someone else can chime in.
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Old 05-08-2015, 08:34 AM   #5
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Originally Posted by Bucko View Post
Eventually, the engine should stumble and stall. That sensor is used to inform the PCM/ECU that pressure at the fuel rails is there, which in turn is used to inform the FPRM (fuel pressure regulator module; the one by the spare tire that has been known to fail due to corrosion) to turn on/off the fuel pump in the fuel tank.
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Old 05-08-2015, 10:04 AM   #6
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Bucko has been drinking again... FPDM Fuel Pump Driver Module
It's Friday...I need to drink more.

I've yet to have an FPDM fail, but then again, my F150's I've owned have never seen salt, snow, or off roading conditions that allow this module's backside to corrode.

However, do our engines have two temp controls (a sender and a sensor)? One for the gauge, and one for the PCM/ECU?
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Old 05-09-2015, 04:44 PM   #7
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Quote:
Originally Posted by Bucko View Post
Eventually, the engine should stumble and stall. That sensor is used to inform the PCM/ECU that pressure at the fuel rails is there, which in turn is used to inform the FPRM (fuel pressure regulator module; the one by the spare tire that has been known to fail due to corrosion) to turn on/off the fuel pump in the fuel tank.
Ok, so how long should it take to stall because it does'nt seem to be anywhere close to doing it and I did replace the FPDM a few months back. Also, fuel pressure always seems to be "good" according to my bluetooth scanner, somewhere around 40 both idling and driving
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Old 05-09-2015, 04:46 PM   #8
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Have you changed the plugs and/or Coil packs ?
Yep, a few months back both motorcraft. I have also pulled the plugs twice to look at them and put my "old" cops back in to see if they would make any difference.....Zilch
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Old 05-09-2015, 04:52 PM   #9
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The warmed engine "immediate start" or "takes longer to start" has me thinking that the PCM/ECU is not getting the correct engine temp reading. On a detected cold engine, the fuel to air mixture is set higher (fuel) to get a cold engine to start, simular to the days of a choke; the choke would cut off air, and allow the fuel mix to be greater.

Once the engine reaches a certain temp, the fuel mixture is lowered, allowing the engine to return to a normal set idle.

Usually an engine today has two temp devices: a temperature sender, used by the cluster temp guage, and a temperature sensor, used by the PCM/ECU to aid in the adjustment of the fuel to air mapping.

My Ford Ranger had this setup, but not sure if these 4.2/4.6/5.4 engines have two temp devices. Perhaps someone else can chime in.
So........... in laymans terms are you pointing me toward something to look at. I agree , it kind of reminds me of the "choke" scenerio and it almost makes me think its "flooded" or not getting enough gas but thats as far as my simple mind can go. It freaking did it today, everytime I drove it and stopped for an errand, it stumbled and slipped to start and then one time started in a millisecond with almost no crank
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Old 05-09-2015, 04:54 PM   #10
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Originally Posted by techrep View Post
Bucko has been drinking again... FPDM Fuel Pump Driver Module
I actually know a bucko and hes a good guy but I knew what this bucko meant. ha ha
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