13 Peterbilt 386 Fuel Gauge Not Reading

Well it depends a little on how it's setup but most likely I'd say one of your vents is plugged and it's returning all the fuel to one side.

Also there is probably a switch on your dash to select left or right fuel tank for the gauge? Are you watching both tanks?

And it's not uncommon for the sending units to read inaccurate. As in showing a quarter but being empty. Probably can be adjusted but it's kind of a pain to do if you can't easily pull the sendor out of the tank on the truck. Just get to know your truck and know that 1/4 means you are on fumes.

And it's fuel, or diesel. Never gas

 

What Lester said is exactly correct.

A quick home (possible) fix...
Remove the return line (runs from top if tank to "T" somewhere under truck. Return line is typically 4 to 6 feet long.)
Cover one side with a rag or towel and blow compressed air thru other side.
If any debris is in line, rag will "catch" it and you will be able to see it.
Do this for both sides.
Also carefully blow air, (remove fuel cap first), into vent on top of fuel tank.
Lastly, remove feed lines, usually located near bottom of tank (should be a shut off valve near bottom of tank. Make sure you shut it off otherwise all your fuel will drain out)
Remove feed line from "T" (some fuel will drain from line)
Again, cover one side with a cloth or rag, and blow compressed air thru other side.
Note... Blow air thru line the opposite way fuel travels.
Blow air into side that connects to the "T" (also called a fuel block)
Reconnect lines, open fuel shut off valve.
There are other possible things that can cause this problem, but this is the most common issue.
Hopefully you got a warranty with your truck.
Skill level... Novice
Time... 1 hour.
Patience level... l high.