hello everyone!

when i first got Sanford, my 1985 F250 (460/4 speed/4x4) i ended up deleting the rear tank and also installing a new in tank fuel pump/ sending unit assembly in the front tank. the fuel pump works flawless, and the gas gauge does move, but the thing i have noticed was that the fuel gauge isnt reading properly.

when the tank is filled up (19 gallon tank) the gauge reads full. After several days of driving, the gauge will work its way down to empty, in a very regular motion, but when i go to fill it up, it only takes 8 gallons to fill it. similarly, if i top it off when the gauge reads half tank, it only takes 4 or 5 gallons to top it off. and finally, over the weekend, while towing the trailer, i drove the truck a solid 70 miles with gauge reading dead empty, and still was only 14 gallons total down when i got home.

Does anyone have thoughts to why this gauge is giving me improper readings??

 

First I would remove the wire/plug and check and clean the contacts.


But I would not be surprised if the sending unit is just worn out. Maybe the resistance strip or contact arm is corroded or loose. I think it is time to buy a new sending unit.


I had a sender in my truck where the brass float was getting fuel inside it and making it heavier - so it would never read completely full, but that is a different symptom than you describe.

 

I vleaned and inspected the plug when i put the new spectracsending unit in 3 months ago. made sure to use dialectric grease too.

 

Okay. Three months is not enough time for a new sending unit to wear out. Maybe it's just a cheap Chinese made unit.

Can you remove it and test it with an Ohmmeter as you move the float arm up and down by hand? The Ohm readings are given in the manual. It could be that at some points in the travel the readings are just wrong (I don't recall the number now, but say empty is 10 Ohms and Full is 100 Ohms, you would expect half tank is around 45-50 Ohms, but maybe your sender has a resistance of 20 Ohms once it drops to half tank so the gauge then drops to near empty.

Or if you have access to a "variable resistor" you could watch your gauge movement with different resistances applied to see if the gauge movement is smooth and consistent. The old "Fuel Gauge" tester we had in the shop had a dial where you would rotate the specified resistance (i.e. 10 or 20 Ohms, etc.) and watch the gauge movement. It would not be hard to make a tester like this. But I think the problem is more likely with the in-tank Sender than with the dash gauge.

Good luck.

 

The range should be 10-12 ohms at full and 72 ohms at empty. But there's about an amp of current at Full, so you'll need a 10 watt resistor to test with or the resistor will burn up pretty quickly.

It sounds like you have the wrong sending unit. Maybe one for a smaller tank? You can bend the arm to adjust things a bit, like at what point it hits Full. But that also adjusts where it hits Empty, and what you need to do is to adjust the range - make it wider. I don't think you can do that without making the arm the float is on longer.

 

Funny, my truck does this same exact thing

 

subscribed

 

Spectra Part Number; ?

Electric or Mechanical Fuel Pump ?

Do you have a part number off the one you replaced ?

 

The one i had pulled out was rusty, abd original.

Its an electric pump, ill get a part number tonight after work.

 

You may never get it to read exact. few of the trucks I have had do. The 89 I have now, the rear tank was pretty good, the front tank reads full for a long time and starts falling quickly. And when it reads near empty you had better be looking for a fuel station.

If you take it out, I would try to monkey with the arm/float assembly and try to get it to read accurately at the bottom which is most important. When it is sitting on the stop, I like for it to read empty, and that should leave you 2-3 gallons in the tank as a reserve. So when you go to fill you usually never get near 19 gallons in the tank, more like 15 gallons.

 

I was wondering if I would even bother trying to get them to work better. It's low on the list anyway.

 

Were you able to match them up to see if they were the same length?

And if the float arm was the same length and angle?

 

yup me too, way more things that dont work at all

 

Like a radio, a finicky gauge will drive you a little crazy but you should hear my singin

 

I've got the same issue on my 86' XLT Lariat. I replaced both sending units with Spectra premium units (Rear-FG33B, Midship-FG34C). The old units were the original ones & both brass floats had pinholes. Even after replacing them, I'm still having the same issue. First thought was to bend the float arm, but was advised not to by 2 seperate mechanics. Subscribed & Thank you for posting this!!