Fuel Pressure - I'm at a loss...

[ArcticDingo]

Hey all,

I've been fighting a fuel pressure problem and after replacing pretty much everything I'm now at a loss...

I have been having fuel pressure issues with the mechanical lift pump. An example would be only seeing 2 psi after the filter (this is now mechanical pump #3). Because of this I took the plunge and swapped over to an e-pump as I think the cam lobe on the crank to run the mechanical pump may be worn. I wont know until rebuild time. After countless hours of reading I decided on the Facet Carrier. Pump install when as expected with no issue and I now have great fuel pressure sitting around 9.5 psi at an idle after the filter. The trouble is that as soon as the truck starts moving the pressure drops to 5 psi which really is nothing to complain about but as soon as I start getting up around the 2000 RPM mark the pressure drops off to 0 psi. It pops right back up as soon as I let off the throttle. All of this running empty I can only imagine it will be worse when I get loaded up with the holiday trailer and toy trailer hooked up.

I replace the filter thinking that maybe it was plugging it up with no change. Change the filter again putting the factory style with the removable drain bowl back on again with no change. I have replaces all of the soft lines even thought they were only about 2 years old. I have remove the hard lines and replaced them with soft ones. All of this with no change.

Does anyone have any thoughts or suggestions? Am I worrying about nothing? Should I be cutting my losses and investing in a Holly Red? I have already lost my Moose Junior to a heat soak issue that I believe was cause by lack of fuel when mechanical lift pump #1 failed on a 2600 km trip to the middle of nowhere...

 

[fsmyth]

Sounds like a restriction on the suction side. Maybe some junk in the pickup tube?
Easy to check: blow the line backwards from the lift pump intake. If it clears up,
that was it.

 

[OLDBULL8]

I doubt very much that the Cam lobe is worn that much, they are hardened. Are you sure that you put the pump arm on the underside of the cam? On top of the cam it will pump some. Installing 3 pumps leads me to that question.

You certainly didn't replace the hard lines from IP to injectors?

As fsmyth said above, you just have to be suction restricted.

 

[IDIoit]

you have pressure mixed up with flow.
initial fuel pressure should be between 5-9 psi at idle.
once your JR is told to eat, its like the cookie monster and will eat it up.

i have ran a facet without success. i got a bad pump, and the provider left me screwed,
i went to a holley red, but i dont like the pressure, 4-5 psi.
im going with a holley black regulated down to 8, after my cam install.

 

[icanfixall]

Well seems like you have been doing everything but whats wrong. My guess is the fuel tank switching valve might have some old suction head parts blocking it. Most if not all our fuel tank suction head screens fail and break up into tiny pieces. then they get sucked into the line and stop in the tank switching valve. Have yo ever removed both tanks and cleaned out the suction heads or repaired the suction heads to reach the bottom of the tank. As for blowing back into the tanks. Well that will clear the lines for a time. But if the crap was sucked up once its sure to happen again.

 

[junk]

I'm with the other guys. Sounds like some sort of restriction in the lines. I'm guessing if you blow back through them between the tank and the lift pump you can dislodge the obstruction.

My thought is the electric can overcome the obstruction at idle when flow is less, but once you open her up it can't pull enough fuel around the obstruction to keep up the pressure.

Good luck!

 

[IH444t]

My truck was doing the same thing, so i pulled the bed off yesterday pulled the sending unit out and the showerhead was in a million pieces, I pumped out all the diesel and used a vacumm to get most of the crap out and all the big pieces. I almost forgot the most important part I blew out the supply line of sending unit into a towel and a big chunck of shower head came out and that was my problem with the low fuel. I drove it around and no filter light.

 

[ArcticDingo]

Thanks all! I haven't had much time to look at it since posting. I managed to do a flow test on the pump last night and came up with it flowing at what its spec'd at.

I just got the word from work that I get to go spend the next month in Turkey departing Friday morning. Bunch to do in preparation before I go but I'm hoping to find some time on this before going. Even if its a jug in the back....

I will be working through everyone's ideas.

Much appreciated!

To be continued....