6.4 tricky fuel question - Ford Powerstroke Diesel Forum
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post #1 of 40 Old 05-10-2019, 09:45 AM Thread Starter
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6.4 tricky fuel question

I have a situation with a truck I'm trying to fix up. I have a cranking but no start situation. Changed all the filters and the 2 fuel pumps. bled with proper tools (low side and high side). Ran injector test successfully a couple of times. I have FRP at 0 psi and .50 volts. When I crank desired pressure is 5k psi, actual remain at absolute zero. doesn't move at all. The 0.5 volts tells me the sensor might be ok but what could prevent any pressure to be built up at all!
Question 1: Could FRP sensor still be bad even if the 0 psi pressure voltage (0.49 to 0.51 volts) is good?
Question 2: Could a stuck open injector bring the pressure all the way down to 0 psi (no pressure build up at all, zero!!!!). I find it had to believe.....not a big hole down there! I don't have white smoke coming out of exhaust either. But that could still be mysterious hence next question.
Question 3: My understanding is that injectors need 5k psi to "be cracked open", is that mechanical or is the computer not sending injector opening signals until desired and actual pressure are same or that it reaches the 5k psi on startup.... I'm guessing the signal still goes through but if it didn't that would explain why a malfunctioning FRP that is reading zero at all times prevent startup even if pressure is building up properly in the rails.....

Appreciate you guys help. I will probably end up changing FRP sensor for good measure but it's good time to learn more anyway.....I don't like to throw parts at a problem anyway, I like to diagnose properly and fix accordingly.....
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post #2 of 40 Old 05-10-2019, 12:27 PM
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Let me start by saying... I don;t own a 6.4. They scare me. Keep that in mind when reading my responses below.

Quote:
Originally Posted by killerpitou View Post
Question 1: Could FRP sensor still be bad even if the 0 psi pressure voltage (0.49 to 0.51 volts) is good?
It is possible. Probably not the most popular mode of failure, but possible.



Quote:
Originally Posted by killerpitou View Post
Question 2: Could a stuck open injector bring the pressure all the way down to 0 psi?...
That seems very unlikely to me also. You'd see something.

Quote:
Originally Posted by killerpitou View Post
Question 3: My understanding is that injectors need 5k psi to "be cracked open", is that mechanical or is the computer not sending injector opening signals until desired and actual pressure are same or that it reaches the 5k psi on startup?...
It has to be a system level check. There is nothing about the design of the injector that suggests any need for hydraulic assistance to get going.

With new filters and pumps, a lot has been ruled out. I guess that I'd be looking at whether the engine mounted fuel filter was returning all of my fuel back to the tank. It wouldn't take much error for that 3psi relief valve to starve your HPIF of fuel.




Looking at the diagram... I can't reallly see the check valve on the return line to the cooler causing low pressure at the rails no matter which way it was stuck - if it was. The other valves are internal to the pumps.

I will attach the following:
  • Description of the fuel supply system from the coffee table book
  • Description of the fuel management system from the coffee table book
  • Datasheet for the fuel rail sensor (for testing)
  • Description of the fuel system from the PCED
  • Hard start/No start procedure from the PCED
  • Hard start/No start worksheet from the PCED
  • Pinpoint Test M (Fuel System) from the PCED
  • Pinpoint Test MA (Fuel Pump Control [low]) from the PCED
  • Pinpoint Test MB (Fuel Rail Pressure Sensor) from the PCED
  • Pinpoint Test ME (Fuel Pump Control [high]) from the PCED

This forum only allows 5 attachments per post. So... two posts.
Attached Files
File Type: pdf Powerstroke 64L - Fuel Supply System.pdf (1.29 MB, 12 views)
File Type: pdf Powerstroke 64L - Fuel Management System.pdf (3.13 MB, 13 views)
File Type: pdf Sensor 64L - Fuel Rail Pressure Sensor.pdf (122.4 KB, 12 views)
File Type: pdf 2008 64 PCED - Fuel System.pdf (169.6 KB, 18 views)
File Type: pdf 2008 64 PCED - Hard Start-No Start Diagnostic Procedure.pdf (516.7 KB, 16 views)

2004 F550 CC Lariat
BPD oil cooler relocation and upgraded EGR cooler (spooled), BPD oil bypass filtration, aFe Magnum Force CAI, Mishi radiator, 7.3L fan clutch, EC1 ELC, XDP coolant bypass filtration, '08 trans pan/filter, PTP direct clutch solenoid, blue spring, 6.4 starter, MBRP y-pipe, BD boots/clamps, '05 intake elbow, ccv reroute, Torque Pro + OBDLinkô LX, Autometer EGT
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post #3 of 40 Old 05-10-2019, 12:28 PM
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...and the rest.

2004 F550 CC Lariat
BPD oil cooler relocation and upgraded EGR cooler (spooled), BPD oil bypass filtration, aFe Magnum Force CAI, Mishi radiator, 7.3L fan clutch, EC1 ELC, XDP coolant bypass filtration, '08 trans pan/filter, PTP direct clutch solenoid, blue spring, 6.4 starter, MBRP y-pipe, BD boots/clamps, '05 intake elbow, ccv reroute, Torque Pro + OBDLinkô LX, Autometer EGT
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post #4 of 40 Old 05-10-2019, 12:39 PM Thread Starter
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Quote:
Originally Posted by djmaguire View Post
...and the rest.
djmaguire: Thanks a bunch!!!! that's a lot of studying!!!

One thing I also not understand very well is how using the shredder valve cleans the low pressure side (of air) and the other side of the cooler cleans the high pressure side. Is that just because mechanically the bubbles from the high side all end up there and the ones from the low side end up in front (by shredder)? Because the cooler has no valve in it so it passes through and when you pull gas (and air if you're bleeding....) from either side, pressure should be identical right?
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post #5 of 40 Old 05-10-2019, 12:54 PM Thread Starter
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Quote:
Originally Posted by djmaguire View Post
Let me start by saying... I don;t own a 6.4. They scare me. Keep that in mind when reading my responses below.



It is possible. Probably not the most popular mode of failure, but possible.





That seems very unlikely to me also. You'd see something.



It has to be a system level check. There is nothing about the design of the injector that suggests any need for hydraulic assistance to get going.

With new filters and pumps, a lot has been ruled out. I guess that I'd be looking at whether the engine mounted fuel filter was returning all of my fuel back to the tank. It wouldn't take much error for that 3psi relief valve to starve your HPIF of fuel.




Looking at the diagram... I can't reallly see the check valve on the return line to the cooler causing low pressure at the rails no matter which way it was stuck - if it was. The other valves are internal to the pumps.

I will attach the following:
  • Description of the fuel supply system from the coffee table book
  • Description of the fuel management system from the coffee table book
  • Datasheet for the fuel rail sensor (for testing)
  • Description of the fuel system from the PCED
  • Hard start/No start procedure from the PCED
  • Hard start/No start worksheet from the PCED
  • Pinpoint Test M (Fuel System) from the PCED
  • Pinpoint Test MA (Fuel Pump Control [low]) from the PCED
  • Pinpoint Test MB (Fuel Rail Pressure Sensor) from the PCED
  • Pinpoint Test ME (Fuel Pump Control [high]) from the PCED

This forum only allows 5 attachments per post. So... two posts.
Is the motor mounted filter housing a common failure? I agree that I might have an issue there. I did notice that not as much gas comes out of the high side than low side (fuel cooler) when I turn the pump on. Would the pressure valve in the filter housing malfunctioning cause that symptom?

Last edited by killerpitou; 05-10-2019 at 01:28 PM.
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post #6 of 40 Old 05-10-2019, 02:03 PM
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Quote:
Originally Posted by killerpitou View Post
djmaguire: Thanks a bunch!!!! that's a lot of studying!!!...
Not trying to overload you. I'd just work with the description docs and only go to the long ones if needed.



Quote:
Originally Posted by killerpitou View Post
...One thing I also not understand very well is how using the shredder valve cleans the low pressure side (of air) and the other side of the cooler cleans the high pressure side. Is that just because mechanically the bubbles from the high side all end up there and the ones from the low side end up in front (by shredder)? Because the cooler has no valve in it so it passes through and when you pull gas (and air if you're bleeding....) from either side, pressure should be identical right?
Even with no valve, the internal configuration could make a difference. If the fuel inlet and outlet - internally - are tubes that go to the lower part of the cooler, air could get trapped in there on one side ot the other that could only be released by letting it go at that particular connection. We tend to think as ports as ending at the enclosure. There could be a lot going on inside beyond even the passages.


Quote:
Originally Posted by killerpitou View Post
Is the motor mounted filter housing a common failure? I agree that I might have an issue there. I did notice that not as much gas comes out of the high side than low side (fuel cooler) when I turn the pump on. Would the pressure valve in the filter housing malfunctioning cause that symptom?
Not sure about common. ...and can't say whether the difference is a symptom or not.

___________________
Edited to add...
I noticed that one of my PDFs didn't start on the correct page. Attaching the corrected version.
Attached Files
File Type: pdf Powerstroke 64L - Fuel Management System.pdf (2.14 MB, 8 views)

2004 F550 CC Lariat
BPD oil cooler relocation and upgraded EGR cooler (spooled), BPD oil bypass filtration, aFe Magnum Force CAI, Mishi radiator, 7.3L fan clutch, EC1 ELC, XDP coolant bypass filtration, '08 trans pan/filter, PTP direct clutch solenoid, blue spring, 6.4 starter, MBRP y-pipe, BD boots/clamps, '05 intake elbow, ccv reroute, Torque Pro + OBDLinkô LX, Autometer EGT
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post #7 of 40 Old 05-10-2019, 02:09 PM Thread Starter
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Quote:
Originally Posted by djmaguire View Post
Not trying to overload you. I'd just work with the description docs and only go to the long ones if needed.





Even with no valve, the internal configuration could make a difference. If the fuel inlet and outlet - internally - are tubes that go to the lower part of the cooler, air could get trapped in there on one side ot the other that could only be released by letting it go at that particular connection. We tend to think as ports as ending at the enclosure. There could be a lot going on inside beyond even the passages.




Not sure about common. ...and can't say whether the difference is a symptom or not.

___________________
Edited to add...
I noticed that one of my PDFs didn't start on the correct page. Attaching the corrected version.
I guess I'm going to change the FRP sensor so I can get a trustworthy idea whether there is really zero in there.... I don't know how sensitive these are. When I removed the tubes from pump to rails after a test I noticed there was some pressure relief in there....So I have some pressure. Don't know how little is too little to be measured by the sensor, considering the range is from 0 to 25k psi..... +/- what????

Are you suggesting from your previous answer that the computer will not fire the injectors if the rail pressure is not up to par???? My basic understanding from "cracking open" is that under the 5k psi, the injector could not physically fire, as opposed to the injector will not fire (because of ECU....)
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post #8 of 40 Old 05-10-2019, 02:35 PM
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Yes a hung injector will reduce pressure to zero. Injectors hanger because of debris.

Likely your pump ate itself. Check the bottom of the fuel filter bowl for metallic sparkles.
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post #9 of 40 Old 05-10-2019, 02:59 PM Thread Starter
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Quote:
Originally Posted by SOOTIE View Post
Yes a hung injector will reduce pressure to zero. Injectors hanger because of debris.

Likely your pump ate itself. Check the bottom of the fuel filter bowl for metallic sparkles.
Bottom of filter was never spoiled with metal shavings. I will take a line off of an injector and pour the fuel in it into a container and check for shavings there.

I thought a clogged injector from metal shavings makes the pressure go higher, not lower (stuck open). Does metal shavings in the injector would make the buzz test fail? Mine are all successful. I truly believe the hpfp never failed mechanically. I've pulled the fuel from the cooler too and it was clean as well.
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post #10 of 40 Old 05-10-2019, 03:02 PM
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Quote:
Originally Posted by killerpitou View Post
Bottom of filter was never spoiled with metal shavings. I will take a line off of an injector and pour the fuel in it into a container and check for shavings there.



I thought a clogged injector from metal shavings makes the pressure go higher, not lower (stuck open). Does metal shavings in the injector would make the buzz test fail? Mine are all successful. I truly believe the hpfp never failed mechanically. I've pulled the fuel from the cooler too and it was clean as well.
No such thing as a buzz test on a common rail. Injectors hang open from debris not shut. Aka open nozzle = no pressure
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