[massmayhem]

So today I installed my DIY big hose fuel line from the fuel filter canister to the cp3 with a fuel pressure gauge. At idle it shows between 8 and 10 psi and between 8 and 9 psi when cruising down the highway. Although once I go to WOT the pressure drops to about 4 to 6 psi, is this normal? Or is it a sign of a weak lift pump? Not that it really matters at this point, on the 15th I'm getting a FASS 95/150 lift pump installed, I'm more curious as to if it's a sign of a pump getting weak or if that's a normal pressure drop. I had a shop tell me that the lift pump is getting weak, but I have no clue what pressure a stock pump runs at and what kind of pressure drops are associated with throttle positioning.

 

[Rabbler]

Sounds about right. How many miles on the fuel filter?

The In-tank pumps are higher volume but lower pressure than the previous years.

 

[massmayhem]

Brand new, changed it at the same time as when I put in my big hose from the fuel filter canister to the cp3.

 

[rocket]

You can't just put a big line between the canister and cp3. You have to run the same size hose from the tank...and make sure to use -AN fittings rather than banjo bolts...

The little line cannot keep up so you have low pressures at that point.

 

[massmayhem]

Ah ok makes sense. As for running the same size line from the tank, in a couple weeks I'm getting a FASS 95/150 installed, so at that point I will have the the same size line from the tank up. I did use -AN fittings too, Russell Performance Full Flow fittings.

 

[massmayhem]

Just one thing I noticed though when I was going about all this, my return line on the back side of the fuel canister runs up into the back side of the head of the motor. Anyone know it's purpose?

 

[NickBeek]

Fuel return from the injectors.

 

[rocket]

................

 

[massmayhem]

the fuel return for the pop-off valve(which is capped) runs to the front side of the fuel filter canister then through a hole on the canister to the line on the backside of it. i'm more curious of the backside line running up to backside of the head. I guess i could just pull the cover off and see if it does connect to the injectors, but i don't really feel like doing that tonight lol.

 

[Rabbler]

Your answer is in post #7.
That's the return fuel pipe from all the injectors.
Not all the fuel sent from the HPCR is injected in to the engine.
A portion of the fuel is returned back to the fuel supply system.

 

[massmayhem]

So is it actually neccesary to have this return line? Or is it just a rail pressure killer like the pop-off valve when it begins leaking?

 

[Rabbler]

It has to be there. I don't think the injectors can fire if you cap it.
This return fuel actually helps cool and lubricate the injectors. Its designed to work that way. Don't worry about it :cool019:

 

[massmayhem]

LOL k, I was just curious as to it's being lol. So does the same go for the tie-in from the cp3 to the return line? More curiousity here, trying to learn as much as I can on how the cummins works and all that good stuff.

 

[Rabbler]

Ya same kind of deal for the CP3.
About 50% of the fuel supplied to the CP3 is routed to the return like to keep it cool and lubricated.
That hex head plug on the top of the CP3 is called the "cascade overflow valve" it regulates how much fuel goes to the return line.

 

[massmayhem]

Wow 50% Didn't think it was that much, i thought it was more of a pressure relief for the inside of the cp3. So I'm just going to run with a little idea here, might be a kinda stupid or redundant idea, but what if instead of allowing the the return lines from the cp3 and the injectors to return the fuel back to the tank, instead re-enter them pre-cp3 on the supply line with check valves to keep the lift pump from trying to force fuel through those lines to help keep supply pressure to cp3 up?