Can't prime fuel lines.

[jefjoc]

I have broke open fuel line below the lift pump and applied 40 psi to the tank which is full, yet i don't get fuel flowing from the open line. Any suggestions on what may be the cause? Thanks

 

[Valley Rock]

Process of elimination, start near the source .

Undo the fuel outlet line at the top of the tank and see if it comes out there, then go from there .

40psi is way too much imo, I would say 10 psi would be more than enough provided the vents on top of the tank are plugged so that the added pressure actually goes out the output line instead of the vents .

 

[jefjoc]

Thanks for the reply. This may suprise you but I turned up compressor to 100 psi. That allowed fuel to flow through the line up to lift pump, but from that point on I was unable to get flow coming out of injector pump bleeder screw inspired many attempts with compressor. I have to figure out where the blockage is from lift pump forward.

 

[G744]

You're lucky you didn't rupture your fuel tank with 100psi.

 

[jefjoc]

With a full tank of fuel there is little space to apply pressure. What found is the new lift pump is defective.

 

[gringeltaube]

With a full tank of fuel there is little space to apply pressure.

Safety first! You sure had a large pan placed underneath your tank, to catch up to 80 gallons of diesel right...?

You were very lucky: normally, fuel tanks are pressure tested at 5psi maximum. 100 psi is more than enough to cause any fuel tank to permanently deform and most likely, crack open!
And even a "full tank" - pumped up to that kind of pressure - will hold enough air for it to eventually expand violently... AKA explosion!

 

[jefjoc]

It was a small compressor and a full tank. 100 psi was momentary

 

[WillWagner]

It was a small compressor and a full tank. 100 psi was momentary

Doesn't matter how "momentary" it was. The system isn't designed for 100 psi.

There are two check valves in the lift pump, one in the inlet, the other in the outlet, they are identical, just installed opposite each other. You can remove the threaded outlet port, and look at the valve to see if it is backwards, careful, there is a spring under it. If so, turn it around, should be GTG. RELEASE ANY PRESSURE IN THE TANK BEFORE STARTING ANY WORK.

 

[jefjoc]

Thanks for the info. A replacement pump is being sent. I'll take a look at the one I remove.

 

[jefjoc]

FYI, I started out with 20 psi then 40 & 60 psi. I could not get flow out of the line I broke open under the loft pump. That is why I put 100 psi in. There maybe a problem with the line not sure. Thanks

 

[smoke]

I would check your pickup tube in the tank. They like to crack right at the top. Just my 2 cents

 

[WillWagner]

A crack in the line would leak pressure and vent out of the tank vent. IIRC, he stated that fuel got to the LP but nuttin' out. COULD have a POS in the inlet of the pump. I have seen that before. A piece of debris in the fitting that is replaced when the pump is changed, unseen by the guy that condemned the lift pump.

 

[jefjoc]

Thanks, I thought about the pick up tube. What a headache that would be on this truck.

 

[smoke]

A crack in the line would leak pressure and vent out of the tank vent. IIRC, he stated that fuel got to the LP but nuttin' out. COULD have a POS in the inlet of the pump. I have seen that before. A piece of debris in the fitting that is replaced when the pump is changed, unseen by the guy that condemned the lift pump.

Could be that. Reason I said crack tube because op said he had to put a lot of pressure on tank to even get to flow to lift pump.

 

[Jbulach]

Thanks, I thought about the pick up tube. What a headache that would be on this truck.

Does your truck have the big canister fuel filter behind the drivers front wheel? Exactly how did you pressurize the tank with air, through the tank vent lines, drill and install a fitting in the fuel cap, or something else?

 

[jefjoc]

I modified a fuel cap

 

[Valley Rock]

Thanks, I thought about the pick up tube. What a headache that would be on this truck.

How ?

Even if there are things above the tank that prevent you from removing the tube out, dropping the entire tank is like a 30 min job tops with a beer break .

Hopefully someone didn't run bio fuel in your truck and turn everything including the injector pump into an entire rusty gooey mess like mine, I had to pull my pump apart and clean it all out, bio fuel loves to hang out with water, no bueno .

ATF in the diesel is your friend, well I'll speak for myself and say it is definetly my friend and a friend to my trucks engine .

 

[jefjoc]

Thanks. Problem with that is the tank is full. Avery heavy job including opening fuel lines to accommodate that. Think much easier to use a hole saw above tube.

 

[Jbulach]

Fortunately the tank has two vent lines on it and is the reason you had to, and where able to turn your compressor up so high. IIRC 1 PSI will push fuel up over two feet, so you only need a couple psi in the fuel tank to push fuel higher than the top of your engine, unless you have a blockage in the fuel outlet or canister filter, 3-4 psi will start to make these tanks swell, pop and bang. I use a push tee and low pressure regulator/gauge to control and monitor the pressure in the fuel tank.
I would bet the rupture pressure on these tanks is 10 psi or less, no matter how much fuel is in it. Pressurizing with air or liquid does not effect the rupture psi, only the violence of the failure, plus you can only fill an A2 tank to approximately 80% of it’s actual volume with fuel through the fill cap.

Your problem is not likely a pickup tube or you would have pushed air or bubbling fuel out the fuel line.

 

[Valley Rock]

O

Thanks. Problem with that is the tank is full. Avery heavy job including opening fuel lines to accommodate that. Think much easier to use a hole saw above tube.

The fuel tanks in my 5 ton have a drain on the bottom, pretty handy .