Fuel gauge won't read below 1/2 tank, electrical or mechanical issue?

[BRetty]

All,

My fuel gauge has been wonky since I got my 73 C10. (A 73 that actually has an 81 dash and engine/trans)

It reads correctly above 5/8 of a tank up to full. Below 5/8, it just sticks at 5/8. I've run out of gas a few times, mostly because I was in denial about my gas mileage being ~5mpg.

So I replaced the sending unit a few months ago. I checked the new unit before I installed it, it read 0-89 ohms as I moved the float, just like it should.

So I installed it, but I actually had about half a tank at the time, so it just went to 9/16 this time. We had cut out a random loop of extra wire in the sending line.

Same problem. Tonight I finally got the bed moved back and checked it at the tank. It's reading 47-48 ohms, despite I think I am below 1/4 tank.

Is it possible there is a blockage in the tank that is holding up the float?

I will run a ground right from the battery as a last check, but next I guess I open the tank and peer inside.

BR

 

[Vbb199]

Wrong tank/sending unit combo?
As in wrong gallons to wrong sending unit.


If you checked and got 0-90 range prior, id think elsewhere.....

The same 0-90 range is used until like, the 90s i think

 

[75gmck25]

I’m using Autozone sending units in my ‘75 GMC and they seem to work fine with the stock gauge. However, they are not very linear as the fuel goes down in the tank.

I have learned that I can go from 1/4 tank to out of gas in a very short time. However, I’ve never measured the resistance as it drops, so I don’t know how low it goes.

 

[BRetty]

Thanks for the replies, I'm gonna take the sending unit out this aftn and check the travel on it.

 

[BRetty]

So I have found the problem I think. There's a vertical baffle in the tank right where the sender drops in. The float rests on it when level gets to ~half.

this pic shows the black float and the ridge in the tank:

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There's no way to rotate the sender, there are locking tabs and slots. I could try to cut out the baffle. Flipping around the float is unlikely it's a bent wire that would be destroyed before it could be modified.

Guess I'll look for a different sending unit that gas the float on the other side. This unit is a Spectre.

You must be registered for see images attach

 

[Dleslie212]

Back when I changed both my sending units, I believe they were sold separately for drivers side and passenger side. Maybe you got the wrong one?

 

[Vbb199]

I believe that baffling indicates you have a 87 tank

 

[BRetty]

I believe that baffling indicates you have a 87 tank

Ah, that's entirely possible. Tank is PO replacement, I never deciphered the upside-down yellow paint marker notes on it from the parts yard. Might also be why my filler neck is squished and kinda choked.

I'll look for a sending unit for an 87. Thanks!

 

[Albrigap]

Rarely, like never, is a fuel gauge problem in the gauge.
Virtually always the tank sender or occasionally a bad wire or ground.