fuel pressure test
05-05-2015, 05:52 PM
#3
Senior Member
I thought the 5.4L had one. As to the above post, the reason he wants to physically check the fuel pressure is something in the system has gone bonkers and he doesn't trust the OBD readings at this point.
I dearly hope you don't have the issue I did when my FPDM went south, it took out the PCM, it didn't want to die alone.
I dearly hope you don't have the issue I did when my FPDM went south, it took out the PCM, it didn't want to die alone.
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chiett (05-05-2015)
05-05-2015, 06:45 PM
#4
I thought the 5.4L had one. As to the above post, the reason he wants to physically check the fuel pressure is something in the system has gone bonkers and he doesn't trust the OBD readings at this point.
I dearly hope you don't have the issue I did when my FPDM went south, it took out the PCM, it didn't want to die alone.
I dearly hope you don't have the issue I did when my FPDM went south, it took out the PCM, it didn't want to die alone.
05-05-2015, 06:54 PM
#5
Senior Member
Yep, it is.
After I replaced it I was still getting the same symptoms, took it to my local garage. Local garage looked at it and were getting the same flaky fuel pressure readings you are.
They couldn't get any further with their snap-on reader, and recommended I take it to the dealership. I did so, and found out that the shorting when the FPDM went south fried the entire computer for the engine.
After I replaced it I was still getting the same symptoms, took it to my local garage. Local garage looked at it and were getting the same flaky fuel pressure readings you are.
They couldn't get any further with their snap-on reader, and recommended I take it to the dealership. I did so, and found out that the shorting when the FPDM went south fried the entire computer for the engine.
05-05-2015, 07:33 PM
#6
Yep, it is.
After I replaced it I was still getting the same symptoms, took it to my local garage. Local garage looked at it and were getting the same flaky fuel pressure readings you are.
They couldn't get any further with their snap-on reader, and recommended I take it to the dealership. I did so, and found out that the shorting when the FPDM went south fried the entire computer for the engine.
After I replaced it I was still getting the same symptoms, took it to my local garage. Local garage looked at it and were getting the same flaky fuel pressure readings you are.
They couldn't get any further with their snap-on reader, and recommended I take it to the dealership. I did so, and found out that the shorting when the FPDM went south fried the entire computer for the engine.
i have one of those edge evolution programers in it and i just used it to check my throttle position sensor, is there anything else i can use it to check that will give me a new place to start looking for the problem?
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05-05-2015, 07:55 PM
#8
i just did what i believe is called a back probe test on the sensor its self,and i get 5 volts reading on one pin which is correct but i get a 4.5 volt reading on another which i'm not sure is right. the out signal should read zero unless i am moving the throttle right.
05-06-2015, 01:38 AM
#9
LightningRod
[MENTION=208187]chiett[/MENTION]
I didn't get the same message out of your initial post as [MENTION=22971]gone postal[/MENTION], who said:
I wasn't trying to be a smart ***. I really did want to be helpful. But I also haven't seen any specific symptom or problem or specific "same flaky fuel pressure readings" to work with. What are the symptoms and what is the OBDII fuel pressure reading? Heaven help us if the OBDII readings can't be trusted. The poor PCM has nothing else to work with - so what is the PCM doing with that "untrusted" fuel pressure reading. ie: Any codes set? Are short term fuel trims Positive or Negative? Are the upstream O2 sensors operating too rich or lean. What is the Fuel Pump duty cycle? What is manifold vacuum - (because fuel rail pressure is modulated based upon it)? All these sensors and control parameters are interrelated and one "flaky" one will inevitably show up as over compensation in another. Having said that - WHAT does the throttle position sensor have to do with any of this at this point?
And finally ---- NO, none of the readers or scanners read the actual sensors. The PCM reads the sensor, messages the reading - does number crunching on it - and stuffs the result in a "mail box" with a specific Perameter ID and there it sits until a reader requests the value stored in that mail box. (that is a gross over simplification because this stuff is happening like at millions of times per second). Also, in many instances there is not even a physical sensor out there for a given representation presented by the ECU. Such is the case on the 5.4L with engine coolant temperature. The ECU reads the Cyl Head Temp sensor, calculates engine coolant temperature and stores that as ECT (PID # 1139). Even though there's not even a coolant temperature sensor anywhere, your scanner can read BOTH!
In any event - since it seems you have a reader (I'm not familiar with the Edge), it is still most efficient to read and challenge the various related sensors or parameters. Does the fuel rail pressure change when you unplug vacuum from it, or apply more suction on the fuel pressure sensor's vacuum reference port - ect, ect?
Good luck
I didn't get the same message out of your initial post as [MENTION=22971]gone postal[/MENTION], who said:
And finally ---- NO, none of the readers or scanners read the actual sensors. The PCM reads the sensor, messages the reading - does number crunching on it - and stuffs the result in a "mail box" with a specific Perameter ID and there it sits until a reader requests the value stored in that mail box. (that is a gross over simplification because this stuff is happening like at millions of times per second). Also, in many instances there is not even a physical sensor out there for a given representation presented by the ECU. Such is the case on the 5.4L with engine coolant temperature. The ECU reads the Cyl Head Temp sensor, calculates engine coolant temperature and stores that as ECT (PID # 1139). Even though there's not even a coolant temperature sensor anywhere, your scanner can read BOTH!
In any event - since it seems you have a reader (I'm not familiar with the Edge), it is still most efficient to read and challenge the various related sensors or parameters. Does the fuel rail pressure change when you unplug vacuum from it, or apply more suction on the fuel pressure sensor's vacuum reference port - ect, ect?
Good luck
05-06-2015, 09:08 AM
#10
@chiett
I didn't get the same message out of your initial post as @gone postal, who said:
I wasn't trying to be a smart ***. I really did want to be helpful. But I also haven't seen any specific symptom or problem or specific "same flaky fuel pressure readings" to work with. What are the symptoms and what is the OBDII fuel pressure reading? Heaven help us if the OBDII readings can't be trusted. The poor PCM has nothing else to work with - so what is the PCM doing with that "untrusted" fuel pressure reading. ie: Any codes set? Are short term fuel trims Positive or Negative? Are the upstream O2 sensors operating too rich or lean. What is the Fuel Pump duty cycle? What is manifold vacuum - (because fuel rail pressure is modulated based upon it)? All these sensors and control parameters are interrelated and one "flaky" one will inevitably show up as over compensation in another. Having said that - WHAT does the throttle position sensor have to do with any of this at this point?
And finally ---- NO, none of the readers or scanners read the actual sensors. The PCM reads the sensor, messages the reading - does number crunching on it - and stuffs the result in a "mail box" with a specific Perameter ID and there it sits until a reader requests the value stored in that mail box. (that is a gross over simplification because this stuff is happening like at millions of times per second). Also, in many instances there is not even a physical sensor out there for a given representation presented by the ECU. Such is the case on the 5.4L with engine coolant temperature. The ECU reads the Cyl Head Temp sensor, calculates engine coolant temperature and stores that as ECT (PID # 1139). Even though there's not even a coolant temperature sensor anywhere, your scanner can read BOTH!
In any event - since it seems you have a reader (I'm not familiar with the Edge), it is still most efficient to read and challenge the various related sensors or parameters. Does the fuel rail pressure change when you unplug vacuum from it, or apply more suction on the fuel pressure sensor's vacuum reference port - ect, ect?
Good luck
I didn't get the same message out of your initial post as @gone postal, who said:
I wasn't trying to be a smart ***. I really did want to be helpful. But I also haven't seen any specific symptom or problem or specific "same flaky fuel pressure readings" to work with. What are the symptoms and what is the OBDII fuel pressure reading? Heaven help us if the OBDII readings can't be trusted. The poor PCM has nothing else to work with - so what is the PCM doing with that "untrusted" fuel pressure reading. ie: Any codes set? Are short term fuel trims Positive or Negative? Are the upstream O2 sensors operating too rich or lean. What is the Fuel Pump duty cycle? What is manifold vacuum - (because fuel rail pressure is modulated based upon it)? All these sensors and control parameters are interrelated and one "flaky" one will inevitably show up as over compensation in another. Having said that - WHAT does the throttle position sensor have to do with any of this at this point?
And finally ---- NO, none of the readers or scanners read the actual sensors. The PCM reads the sensor, messages the reading - does number crunching on it - and stuffs the result in a "mail box" with a specific Perameter ID and there it sits until a reader requests the value stored in that mail box. (that is a gross over simplification because this stuff is happening like at millions of times per second). Also, in many instances there is not even a physical sensor out there for a given representation presented by the ECU. Such is the case on the 5.4L with engine coolant temperature. The ECU reads the Cyl Head Temp sensor, calculates engine coolant temperature and stores that as ECT (PID # 1139). Even though there's not even a coolant temperature sensor anywhere, your scanner can read BOTH!
In any event - since it seems you have a reader (I'm not familiar with the Edge), it is still most efficient to read and challenge the various related sensors or parameters. Does the fuel rail pressure change when you unplug vacuum from it, or apply more suction on the fuel pressure sensor's vacuum reference port - ect, ect?
Good luck
hey Torqued no worry's none taken, when I first started noticing this problem it only happened when head temps where still below 196F, and only when I was pulling out from like a stop light, if I was able to give it a fare amount of throttle it seemed to run fine, but if I was in a 30 mph speed zone according to the edge reader my fuel pressure would start dropping to like 2 psi and than spike to like 58 psi and everything in between, and the truck would start bucking real bad, and every so often it would do it bad enough to pop a code, and they were always related to the emissions and tank pressure, which I wrote off as being a result of the problem not the cause, but now it has completely dyed and will not even fire to start, like its not getting fuel to the plugs, which I am assuming is because according to my edge when I cycle my key to run the fuel pump I am not getting enough fuel pressure, I have a new filter I even went and paid 422 dollars for a new fuel pump and still no pressure. and for the throttle position sensor I was hoping that maybe it was sending a wot signal to the brain which cause it to shut everything down because its not running. lol I am just getting desperate .