New 38 gal tank, air in lines but old 38 gal was fine

[The_Josh_Bear]

So I have dual tanks, a working selector valve and a 38 gallon rear tank.

At some point the current owner that shall remain nameless pulled a bone head move and broke the fill neck cause he forgot to loosen up the only hose clamp that MUST be loosened to drop the tank. So after pulling "just a little harder" it broke loose, literally.

Fast forward to new tank install, everything went well and I zipped her all up. Drove to work fine and came home up the big hill to my house and I ran out of fuel with like 35 gallons in the tank. Happened again the next morning going down my hill.
Runs up and down hills great on the front tank.

What gives?? Does this sound like the FSV is giving up or what? I didn't change or adjust anything with the fuel pickup since it worked great for years in the old 38.

BTW hot tip for the manual transmission boys and girls:
If you run out of fuel going up hill, it's easy to just switch tanks, put it in 2nd gear with the key on and roll-start it, right? Well guess what you do if you're facing up-hill? Put it in reverse and do the same thing! It purges the IP unbelievably fast and I love that trick. And if you don't drive a manual trans then

 

[franklin2]

Those 38 gallon tanks have sending unit pickup extensions correct? Did that happen to fall off when wrestling the tank in place?

 

[IDIBRONCO]

Well guess what you do if you're facing up-hill? Put it in reverse and do the same thing!

I did the same thing with mine when the starter quit working. It made me nervous because I had my slide in camper in the bed and a trailer behind. I had to try that twice to get it running.

Those 38 gallon tanks have sending unit pickup extensions correct? Did that happen to fall off when wrestling the tank in place?

Even if the extension would have fallen off, I doubt that it would have run out of fuel with 35 gallons left in the tank.

 

[Big Bart]

I am in IDIBronco’s camp. Full tank, should not be a pick up tube thing.

Some thoughts.
1) Did you have air trapped somewhere in the system, the angle of the driveway is just making it so it can purge out?
2) Perhaps the vent or return line create issues going up hill? Diesel rushes them because tank is full. Temporarily causing pressure or allowing vacuum to build up.
3) Do you maybe have a kink or a clog in a line. So the fuel pump can suck on level ground but struggles on a hill? Has to pull a little harder or when the pump is higher than the tank it struggles or sucks hard thus creates a air leak and pumps air not fuel?
4) Some how your dual pump system is battling or competing?

Odd one, let us know what you find. I would go back and look for kinks or potential air leaks.

 

[The_Josh_Bear]

Those 38 gallon tanks have sending unit pickup extensions correct? Did that happen to fall off when wrestling the tank in place?

That's something I need to check. I doubt it, but honestly it's the most likely possibility. I tried to check it out the other day and fuel leaked as soon as I broke the seal. So I need to drive a while on the front tank and pump a bunch over to the front tank before trying again.

 

[Old Goat]

Those 38 gallon tanks have sending unit pickup extensions correct? Did that happen to fall off when wrestling the tank in place?

I did the 38G tank couple years ago. The tank come with a bag of parts, bolts, connectors etc.... There is a piece of copper pipe and a compression fitting to lengthen the pick up tube. When it is tight, it isn`t coming off.

I can`t see it coming off once the Sending Unit is installed wrestling the tank in place from under the truck.

Anything is possible I guess.

Goat

 

[The_Josh_Bear]

I was finally able to get after this today, and I'm happy to say the problem was pretty anticlimactic.

As I've read on this site many times, I took some low pressure shop air and blew it back through the supply line from my fuel filter. I made sure the FSV was switched to the rear and it took a little bit but then blew out whatever was clogging it up and she ran great for a 1.5 hour round trip today. Woo!!!

I probably should have disconnected the line at the top of the tank and stuffed that end in a tub or something so the junk didn't go back into the tank. But too late now, guess I'm going fishing some day. Whatever it was clogged the line GOOD. I couldn't even idle 1 min before it would die before.

Fixed!