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Old 10-05-2013, 04:09 PM
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Another Low Fuel Pressure Thread

Hi All,

Long time Lurker, but haven't really posted up much. Anyway, here is what I have going on.

I purchased an '06 F350 CC PSD early last spring. It needed some serious love. If you want to check it out, I covered pretty much everything here:
Project Super Duty

I have put over 10k Miles since I installed the blue spring upgrade kit. Last week, the truck started losing fuel pressure. It used be a solid 65psi at idle and never drop below 58psi @ WOT. It dropped to 50psi at idle/cruising and then steadily down to 35psi over a 30minute drive (I was trying to get home). I figured the filters might have gotten plugged up after some bad fuel, since I had to get fuel at small gas station in the middle of Iowa recently. I swapped the fuel filters, no change... So I ordered a Fuel pump, just the pump and not the whole HFCM. The fuel pressure jumped back up to 55psi, so I thought I was onto something, but after a short drive (15mins) it dropped back down to 40psi. I pulled apart the FPR and checked for cut/damaged o-rings, but everything looked good. I decided to throw in a bb behind the spring to help troubleshoot. After a few cycles of the key, it was up to 60psi. Again, after a short drive and some WOT runs for 5 seconds at a time and it was back down to 40psi. I noticed at WOT it would drop to 20psi sometimes, but sometimes hold at 40psi. If it drops to 20psi and I cut the throttle, it jumps right to 40psi in an instant.

I'm not too sure where to look next. I figured I would drop the tank and see if the pick-up is plugged. Also not sure if there is something that controls voltage to the fuel pump. What voltage should I see at the pump? Any input would be really helpful. I am mechanically inclined, but since I am away from all my tools for a year, I'm not able to due much in-depth diagnosis.

Just as an FYI, I was hoping after all this that there was just something up with my electric Fuel Pressure guage. I installed a mechanical and it reads within 1psi. The fuel system is bone stock.

Thanks in advance!
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Old 10-06-2013, 07:30 AM
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Just as an update. I checked the stand-pipe under the second fuel filter and it isn't broken and appears to be functioning fine.

I figure in theory, if I pull the return line off of the HFCM coming back from the FPR, turn on the key that I should see little to no fuel if the FPR never sees more than 40psi. If there is a lot of fuel coming back in the return line, than I would think something is up with my FPR? If there is a lot of air, maybe that leads to a pick up problem???

I'm at a loss with this one, it doesn't seem like a very complex system, but I could have a plugged line and I'm hoping this will help troubleshoot if that's the case.
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Old 10-06-2013, 06:51 PM
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Worked on the truck again today. I pulled the HFCM and went right through it. There was a little bit of crap in the water separator area, but nothing major. I swapped back to the original pump, just to make sure but still only seeing ~40psi at idle. I'm going to go buy a air compressor tomorrow to try and blow out the lines between the fuel pump and the tank.

I have spent hours looking online for answers, but nothing seems to fit my situation, so many dead-end threads! Next up is ordering another blue spring upgrade kit to ensure the spring isn't collapsing or the plunger isn't messed up (nothing visually wrong) and dropping the tank after blowing out the lines.

Any wiring diagrams on whatever powers the pump (relays, etc.) and voltage expected at the pump would be very helpful.

I really don't have the coin to take this truck into the dealer and would really appreciate anyone's suggestions.
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Old 10-12-2013, 02:26 PM
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Wow, I'm pretty surprised that no one has chimed in.

I will be testing the HFCM voltage getting to the pump and will try dropping the tank enough so that I can get the pick up out.

Any other suggestions would be helpful. I have heard that the o-rings on the fuel rails in the heads can fail. I didn't notice any change in oil level or notice the smell of diesel in the oil, but not sure if I would be able to.
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Old 10-12-2013, 08:56 PM
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Sounds like you may have done what I did when I did my Blue Spring Upgrade. I forgot to put the o ring on the plastic bushing insert that the plunger rides in. Once I put the new o ring in, pressure stays above 55psi all the time now.

https://www.dropbox.com/s/8kfmkgpuqi...Sprng_Inst.jpg
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Old 10-13-2013, 07:35 AM
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Quote:
Originally Posted by PHYRMN View Post
Sounds like you may have done what I did when I did my Blue Spring Upgrade. I forgot to put the o ring on the plastic bushing insert that the plunger rides in. Once I put the new o ring in, pressure stays above 55psi all the time now.

https://www.dropbox.com/s/8kfmkgpuqi...Sprng_Inst.jpg
Thank you for the input, it's appreciated. In the case of my '06, it doesn't use the black insert, the brass plunger fits directly into the FPR body. I've had the blue spring upgrade installed for close to 6 months, so I thought possibly something was stuck between the plunger o-ring and the body of the FPR. No such luck.

I'll be spending some time today troubleshooting and hope to find a plugged sock on the pick up or a restriction in a fuel line.
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Old 10-13-2013, 07:54 AM
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Just a random question, maybe silly question, but how old are the fuel filters? Does your filter in the HFCM have a neck with an o ring on it?
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Old 10-13-2013, 04:49 PM
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Quote:
Originally Posted by PHYRMN View Post
Just a random question, maybe silly question, but how old are the fuel filters? Does your filter in the HFCM have a neck with an o ring on it?
No silly questions are possible at this point. I did throw in new filters of the right type, that was my first thought when I saw the pressure dropping.

I found out what the issue was, it was my gauges...not only my electric gauge, but also my mechanical I used as a back up verification. The sending unit from I electrical gauge appears to be providing bad info. The mechanical gauge had a collapsed hose. I ended up installing the gauge onto the test port of the FPR without the hose, just using an adapter.

Here is the result, Key on Engine off.



The lesson to be learned here is cheap tools, equal expensive problems...
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Old 10-13-2013, 06:28 PM
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That's good news, good job troubleshooting.
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