fuel system sucking air, only on front tank

[Ceejmo]

O.K. , I’ll start with a little information.
1994 F350 7.3
dual tanks
electronic fuel selector valve
Fuel pick up tube mod done to the front tank
the following condition existed before the pick up tube mod was done and yes, the bottom of the tube was broken off.

The truck has the sucking air running syndrome while on the front tank. In other words.... It may or may not run on the front tank. Sometimes it will run for a while on the front and sometimes it will not. Defiantly sucking air.
There is one fuel supply line and one fuel return line going from the engine compartment to the fuel selector valve. From the valve there is a set of lines going to each tank. The lines going from the selector valve to the front tank are about 18" long. Since I am only sucking air on the front tank am I safe to assume that this 18" line or it's connection is the culprit? If so has anyone modified and replaced the quick disconnect fittings at the valve and the permanent connection at the fuel tank? Does a new fuel tank pickup unit include these lines?
The rear tank only holds 18 gallons and needs the pick up tube mod done. So I can only use about 13 gallons before filling it up again. This beast sucks up the fuel as fast as we can put it in the tank. The wife is tired of having to add fuel every 150-175 miles. So, I need to fix the front tank and then mod the rear tank.

 

[Exekiel69]

It may be the fuel pickup or it may be the hoses, I don't think the hoses come with the fp but You can replace them with 1/4 5/16 or 3/8 fuel injection hose.

 

[Diesel JD]

I can tell you for sure that new hoses do not come with the new pickup assy. I don't know why the fuel hose would have to be fuel injection hose. I don't see why it would cause a problem to do away with those funky quick disconnect hoses and just use some of that. Admittedly, the fuel injection stuff will last longer especially if you're burning biodiesel or WVO, but at 7-8 dollars per foot, versus replacement every couple of years...I don't know if its really worth the cost. There isn't that much fuel pressur eon teh supply side. If you have already fixed the fuel pickup then either the fuel to selector valve lines are leaking or your pickup tube mod broke off! I hear you on the need to have both tanks. I usually drive about 160-180 miles before switching tanks or filling up. The thing is I believe those darn gauges even though I know they are inaccurate. Most times I will have 5-8 gallons left in the tank if i switch when its at the E line or a bit to the left of that. But who wants to run out...not me!

 

[icanfixall]

Just replace the quick disconnect fitting and line from the tank to the switch. Or pull the sending unit out again and check it out for a problem. You don't need to drop the front tank to remove the switch-sending unit.

 

[Ceejmo]

Thanks guys,
I got a little too much rain last night to be laying on the ground today so, it'll be a project for latter if and when it dries out.

 

[DLSF350]

leave the lines/hoses alone until you are sure that 90* fittings coming out of the sender/pickup unit aren't rusted through. Mine had a pinhole at the bend and was sucking air. cleaned all the rust and had it brazed - end of problem for $10.

 

[typ4]

The orings in the fittings are replaceble with a small pick, mine were brittle. new orings no air leak. silicone grease or vaseline to lube them for assembly