66 Fuel System Issue

[MarkMach]

I'm restoring a '66 hardtop Bird and have a confusing fuel system issue - Fuel tank looks in great shape from outside clean/no leaks etc.
-I have replaced the Constant Voltage Regulator and Fuel Sending unit (Parts from Ecklers).
-I fill the tank (Fuel visible/coming out fill pipe), and the fuel gauge shows a little over 1/4 tank.
-I drove the car and it ran out of gas/stopped running - I hadn't run it near enough to use a full tank (22 Gal) of gas. I re-filled the tank and it only took approximately 5 gallons of gas to fill it, again fuel coming out/visible in fill tube. Fuel gauge again shows a little over 1/4 tank.
-I drive it a little, it runs out of gas again, fuel gage shows empty, re-fill gas and again it only takes about 5 gallons to fill it.
-I am confused - I would think regardless of what the fuel gage says, if the tank is full I shouldn't "run out" of gas after using approximately 5 gallons, and on the other hand, the gauge goes from about 1/4 full to empty showing the use of about 5 gallons of gas. Any Idea what could be causing this?

I'm new to the forum and T Bird Restoration, any help is greatly appreciated

Mark

[MarkMach]

As a follow up/FYI I will be replacing the fuel sending unit again - just got a new one from Wilsons T Bird Parts. Also, the fuel gauge reading 1/4 tank when its full and the running out of gas after using about 5 gallons may just be coincidence and I have 2 separate issues.
I was also wondering if these gas tanks had some kind of baffle inside that may have broken loose causing the problem.
Mark

[jtschug]

There is no baffle inside.

There is a test in the shop manual which takes the sender out of the circuit. I don’t have it with me and I don’t want to steer you wrong. Just look up that section.

You might have some built up resistance in the wiring with a corroded connector somewhere. That resistance will be read by the gauge as a lower fuel level

[dan42]

Seems this is a fuel pickup problem inside the tank. The problem seems to be is a improperly placed pickup tube that is only submerged about 1/4 way into the fuel. I would start by pulling the the sending unit/fuel pick up out of the tank and re installing it with the proper orientation of the tube.

[vince]

I think you do have two problems. How many of us, in younger years, ran cars with no working gauge until we had time and money to fix?So, the gauge will not stop the car from running but, as Dan suggests, could be a pick up problem. Have you had the chance to check the filter at the fuel pump? If it shows some "dust' and such it might indicate the tank is not as clean as it appears on the outside. That would suggest a harder look in the tank after you pull the pick up/sending unit. Hope you solve it.