I'm trying to get everything in working order on my car. This one has me very aggravated:

The resistance range on the sender checks out O.K. If I hook up the sender out of the tank and move the float/arm, the gauge responds well. Once installed in the tank, it won't move off empty with at least five gallons of gas in the tank. I did replace the cork float with plastic. The float moves freely when set down in a near-full container of gas, with the pick-up at a relatively shallow angle as it would be in the tank.

Should the end of the pick-up go down into the well in the tank? I am using an NOS original strainer.

Thanks in advance for any assistance.

3 hours ago, Charlie Sixtyvista said:

I'm trying to get everything in working order on my car. This one has me very aggravated:

The resistance range on the sender checks out O.K. If I hook up the sender out of the tank and move the float/arm, the gauge responds well. Once installed in the tank, it won't move off empty with at least five gallons of gas in the tank. I did replace the cork float with plastic. The float moves freely when set down in a near-full container of gas, with the pick-up at a relatively shallow angle as it would be in the tank.

Should the end of the pick-up go down into the well in the tank? I am using an NOS original strainer.

Thanks in advance for any assistance.

Charlie, check that your gas tank is earthed properly ! remeber that the sender is a resistor to earth/ negative
you may need to make a earth strap from the sender unit to the body

also have a look in the tank and make sure the float isnt snagging on anything

a scope camera down the filler neck is a great way to check !

Edited May 6May 6 by 64 kiwi boni

I would also check continuity and ohm resistance of the sending wire to the gauge. The float sender should be around 0-90 ohms (if memory serves). If there is no continuity, then you have a break somewhere in your sending wire. As Kiwi mentioned, proper grounding is also important.

As I mentioned, if I have the sender completely out of the tank, but connected to the ground wire and the sending lead, the gauge responds nicely when the float arm is moved. So I would think this eliminates any issue with the sending wire, or with grounding (?).

The resistance range is supposed to be 0-30 on the sender, and it checks out.

I will take a look with a scope from the fill end.

Thanks!

39 minutes ago, Charlie Sixtyvista said:

As I mentioned, if I have the sender completely out of the tank, but connected to the ground wire and the sending lead, the gauge responds nicely when the float arm is moved. So I would think this eliminates any issue with the sending wire, or with grounding (?).

The resistance range is supposed to be 0-30 on the sender, and it checks out.

I will take a look with a scope from the fill end.

Thanks!

Charlie , do a resistance test between the body and the face of the sender unit when it’s in the tank !

That will confirm how go your earth to the sender unit is 👍

You want less than 0.1 ohms

I took the tank down to see how the pick-up was positioned. The tube end was a good bit off the bottom of the tank, and not over the well in the bottom. I assume it is supposed to pick up from the well essentially. I did some bending to get it into the well so the tube end is about 1/4-3/8 in. off the bottom. This took the float almost to the tank floor. (There appears to be a flat area where the float should locate.)

The gauge now appears to be working- it moved off empty to near 1/4 full with five gallons in the tank, and car did not "run out of gas" in a short test trip, which it did earlier with the same fuel level. I added five gallons and the gauge went to about 1/2 full.

I cannot figure out why the end of the pick-up tube would not have been in the correct position. The car has only 28,000 miles. It hadn't been run in 26 years, but that still leaves forty years for something to have been messed with.

I spent countless hours trying to figure this out, but was certainly not thinking of this as a potential problem. Thanks for all of your input.

Well done Charlie !