Still having problems, engine loses power after driving brief distance

[tauteur]

We put a new piece of line straight from the tank to the electrical fuel pump, so there shouldn’t be a check valve issue.

When we start the engine with the return line off of the tank, fuel comes out of the return line, making me believe the return lines not clogged. If the fuel is coming out, the return line and the electrical pump is pumping that would also make me believe that the electrical pump because it’s sending it to the return line that the electrical pump isn’t a problem either, but we haven’t tried to see if the return line is pouring out fuel after, and when the truck starts losing power and bogging down

so I just ran the engine at full throttle while parked until it started bogging down a little, and I took the return line off the tank , and even as the engine was bogging down , there was still fuel coming out of the return

 

[Mogman]

Not that it is the problem but you should always put a filter after the lift pump not before.

 

[tauteur]

Not that it is the problem but you should always put a filter after the lift pump not before.

Isn’t there a second filter, the original water separator, after it? So there’s 2 filters

 

[Mogman]

As a general rule you want as little restriction before the pump as possible, pumps unlike fans generally push better than pull.
Probably not an issue here.
You still have a pickup sock in the tank and the fuel tank vent system to consider (try running with the cap loose)
If the factory filter was VERY contaminated there is also a filter on the IP input, it is not meant to be serviced with the IP in place an is a REAL PITA to do on the truck and the risk of pushing contamination into the IP is very likely, but if you get to a point you are positive there is no fuel delivery or return restriction that could be the problem, it is rare because fuel filter maint. is a top priority with diesel engines

 

[tauteur]

As a general rule you want as little restriction before the pump as possible, pumps unlike fans generally push better than pull.
Probably not an issue here.
You still have a pickup sock in the tank and the fuel tank vent system to consider (try running with the cap loose)
If the factory filter was VERY contaminated there is also a filter on the IP input, it is not meant to be serviced with the IP in place an is a REAL PITA to do on the truck and the risk of pushing contamination into the IP is very likely, but if you get to a point you are positive there is no fuel delivery or return restriction that could be the problem, it is rare because fuel filter maint. is a top priority with diesel engines

I’ve tried with cap off. Also no difference

 

[Mogman]

Since you have access to the fuel line get a fuel pressure gauge that comes with a Tee and put it between the electric pump and the factory filter and watch the pressure when it loses power.
It does not have to be an expensive one.

Car Truck Fuel Pump &Vacuum Tester Carburetor Valve Pressure Test Gauge Tool Set | eBay

Intended for Carburetor Engine. Read engine vacuum to 28" HG. This kit will help you diagnose improper timing, burned or stuck valves, leaking manifold, improper fuel mixture, sticking choke, and more without the use of a pump.

www.ebay.com

 

[TNDRIVER]

View attachment 912082 We put a new piece of line straight from the tank to the electrical fuel pump, so there shouldn’t be a check valve issue.

When we start the engine with the return line off of the tank, fuel comes out of the return line, making me believe the return lines not clogged. If the fuel is coming out, the return line and the electrical pump is pumping that would also make me believe that the electrical pump because it’s sending it to the return line that the electrical pump isn’t a problem either, but we haven’t tried to see if the return line is pouring out fuel after, and when the truck starts losing power and bogging down

so I just ran the engine at full throttle while parked until it started bogging down a little, and I took the return line off the tank , and even as the engine was bogging down , there was still fuel coming out of the return

My opinion , based on my experience, you need to tear down the entire system, tank out, replace the pickup sock if necessary, pressure wash the inside of the tank, new fuel lines and return lines, make sure the mechanical pump is pushing fuel, "remove" the stock fuel filter housing and clean it replace the filter and water separator. There is a screen in the back end of the injection pump the can clog also. The further you stray from a "factory" setup the more unknowns you have, if the "factory" arraignment is clean the things work. I think people would be surprised at what can be in the fuel tanks of these things. If you are new to diesels they need a little "biocide" added occasionally and if you live in the cold part of CA. they need antigel when it gets "cold". I had one of my trucks tanks off twice, I learned the hard way and I have a ton of experience with heavy diesels. Just my 2 cents, free advice is worth what it cost you.