76 Formula Update and Sending unit question

[daleone3]

You guys have been great with helping me do some sorting out and troubleshooting so have another question.
On the 76 Pontiac Formula, have installed new fuel pump, tank and sending unit. Lines are clean and it is running magnitudes better, like a 8000 mile Pontiac should.
Once it was all together, I put in a can full (four gallons) of new fuel and primed the lines and started right up. BUT the fuel gauge is reading below empty. It sits below empty and when started it does not move at all.
I have power at the connection in the truck and the connections on both ends are clean.
The ground was reinstalled where it had been and the surface was clean.
I KNOW now that I should have tested the sending unit prior but I didn't so now trying to sort this out before I go to the knuckle cutting process of lowering the tank.
What is possible that the connection on the top of the tank sending unit may have gotten dislodged though I won't be able to check that until the endoscope arrives that I ordered, figured it was worth $60 to buy before I get too far. I really don't think I dislodged the connection and the ground seems to be fine so is there a way to check the actual fuel gauge without getting in to the dash? Any other suggestions?
My initial thought that being a 21+ gallon tank, the four gallons may not have been enough to raise the float but I don't want to put a ton of fuel in to it in case I need to drop it.....see my problem? I would think that four gallons would raise it enough to create some resistance output at the gauge but not certain.
Any insights in to the path of least resistance?
Thank you a ton.
Scott

[70 copo]

Float might be stuck. 4 gallons would be noticeable I think (1/8th tank likely).

[70 copo]

The following process will require the ignition switch be in the “on” position for troubleshooting a fuel gauge issue. The first place to start is to check the ignition 12 volt power feed at the fuel gauge to see that it is powered up. If you DO NOT have 12 volts ignition on the fuel gauge, check the gauge fuse to see if it is good, and make sure the ignition switch is powering the ignition pink wire on the ignition blade of the switch. If you DO have 12 volts to the fuel gauge, the next step is to remove the fuel sending unit wire, and, with the ignition key “on”, ground the sender wire to a good chassis ground. The fuel gauge should immediately go to empty. Removing the sending unit wire from the chassis ground the fuel gauge should go directly to “full”. If the fuel gauge responds correctly, the fuel gauge and sending unit wire at this point are reacting correctly. Next, check the fuel tank float assembly to see if the grounding terminal on the float assembly has a good grounding point to the chassis. If the ground wire looks good, the problem most likely resides in the fuel tank float assembly, and may need to be replaced.

These are recommendations from American Autowire.

[daleone3]

Originally Posted by 70 copo

Float might be stuck. 4 gallons would be noticeable I think (1/8th tank likely).

That was my thought, filing the tank to 3/4 and maybe "helping it along" if it was a little stuck. It is new and came from Ames, be surprised if it were defective but probably not too surprised. Given the gauge did not move at all was hopeful it was just a quirky thing with the sending unit. I am going to check the wiring at the tank and go back and make sure the ground is good before I get too far down any other path.
Thank you

[70 copo]

We loosened a sticky float when I was a kid with some spirited driving. 1/4 tank of gas!

[daleone3]

Originally Posted by 70 copo

We loosened a sticky float when I was a kid with some spirited driving. 1/4 tank of gas!

That may be the plan. Being the first drive in the car I went pretty easy but the new fuel and components made it run crazy good. Next nice day without rain may try that, get a little "spirited" and run it through the gears. Blast to drive.

[njsteve]

I know in my 75 (same tank as yours) it will read near empty when there is still a quarter tank left. I'll then fill it and it'll only take 15 or 16 gallons (not 21) to fill it till it's spilling out. So you could be too low to read.

Try sticking some siphon hose in the tank and see of that contacts the float and alters the reading at all. Otherwise add another 5 gallons.

[daleone3]

Originally Posted by njsteve

I know in my 75 (same tank as yours) it will read near empty when there is still a quarter tank left. I'll then fill it and it'll only take 15 or 16 gallons (not 21) to fill it till it's spilling out. So you could be too low to read.

Try sticking some siphon hose in the tank and see of that contacts the float and alters the reading at all. Otherwise add another 5 gallons.

Thanks Steve, will try that. I believe prior to getting the car the gauge would sit about E but Pin to empty when the ignition was turned, worth a shot.
Appreciate it.

[70 copo]

If you try to break it loose try 1/4 tank of gas and locate an empty parking lot.

Figure a few segments of a regular Gymkhana course and get it sloshing around in the tank. That should stimulate the float.