My 78 ford is not reading the correct amount i replaced the gauge and the sending unit but still is about a half a tank off. not sure can anyone help???

 

the gauge shows empty when at half tank and not sure why, wrong sending unit?? bad wiring?? wrong gauge?? i am becoming frustrated

 

I have similar problem on my 37 pickup. I have a 10 gal fuel cell in the bed and it reads 1/4 tank when I have 1/2 tank. Maybe the answer to your question can help me as well.

 

I'll move this thread to the correct forum, the 73-79 F100 & Larger. Good luck in figuring it out.

 

its a 78 300i6 so i dont usually worry about running out of gas but i would like it to be better

 

Ever pull apart a fuel sender?

What happens is the resistive windings upon which the float arm wipes have stretched and/or collapsed such that the gauge no longer gives an accurate reading.. it's analogous to pushing long tube socks down around your ankles.

For example, my gauge reads "fast" until halfway on the gauge and then slows waaaay down the rest of the tank. Fewer miles are logged between halfway and full on the gauge but in reality, the physical fuel level, I probably have a 3/4-full fuel tank.

I hope that makes sense.

 

I've always attributed this phenomenon to the shape and taper of the fuel tank.
Lots of fuel tanks taper outward from the top, down to the widest point of the tank, which is around the middle. Many of them tend to taper back inward, from the middle down to the bottom.
As the first (top) half of the tank is consumed, the tank is getting wider, causing the actual level to drop slower and slower, (per a constant rate of consumption) which the fuel gauge indicates.
Plus if the gauge sender is maxed out when the tank is still 7/8ths full, that would explain why the needle waits so long to even begin dropping.
Then as the level drops below the halfway mark, the tank begins to narrow back down, meaning that our constant rate of consumption is dropping the level in the tank faster and faster.
If I were building a car with new parts from summit or where ever, I would test the new sender in the new tank maybe with water, or at least hold it up to the tank at the level the sender is going to sit, and use a jack or something to get a controlled drop and rise of the float, in order to see what it makes the gauge do. You'd rather know before it's been filled with gasoline...

 

Have you had any luck figuring this out? Mine does exactly the same thing. Ive put 2 new sending units in and they all read the same. Ive checked the ohm's and they all read exactly what they are supposed to. But still, I show empty when i have a half tank. I even tried a second gauge cluster.

 

Chexk all the wiring and connectors for corrosion. Any extra bit of resistance will mess up the reading

 

I have not but take a look at this.

https://www.hotrod.com/articles/corr...nts-fuel-link/

 

My first Ford was a 1978 F100 in 1980. I have always driven a Ford truck. Every one of them had the fuel gauge work exactly the same way. The top 1/4 of the tank seemed to last forever, then the next 1/4 or so would go down a bit faster, and the last 1/3 or so would go down rather quick. On empty it seemed I could go another 20 miles or so. To me it’s typical Ford. Get used to it. Once you figure out that when the needle hits 1/4 it’s probably a good time to watch for a gas station. Like was mentioned earlier check the wiring and connections. Sometimes it’s the float. Have fun!

 

Did you check the float height in the tank? The float arm is not necessarily bent at the right angle when new. Check with an empty tank that the float barely clears the bottom of an empty tank. At least on mine, I was able to look in the filler port with a flashlight and see where the float sat at empty and was able to bend the float arm to adjust.

 

Im gonna empty the tank out some, and see if i can "adjust" or bend haha the float arm to make it a bit more correct. Mine reads below empty with 10 gallons left in a 19 gallon tank. Ive owned a lot of fords, but never had one quite this far off. haha

 

I too have this issue. My old sender was all over the place. I installed a new unit, I think it was a Spectra from Advance Auto Parts. It reads full like it should and when it gets to empty, I always have 9 gallons left. Every time! I think I remember seeing in a post, here or somewhere, that the Spectra brand units were likely to have this problem. I just have never taken the time to remove the tank and bend the arm. I guess I'd rather have a lot of reserve at empty then to run out. But when I get to half a tank, I know I have used 5.5 gallons. It's very consistent all throughout the range.

 

My gauge is off about an 1/8 tank or so ( reads lower than true level) . Don't know if I will ever bother ****ing the sender since that is a big job to drop the tank and stuff, a bit above my comfort level