Is there a way to adjust the gas gauge reading?

My '66 F100 shows 3/4 full when it is full.

 

Is it actually empty when it says empty? Mine does the same exept it reads just over half a tank when full and I still have almost 8 gallons when it reads empty

 

It has about a gallon when it is on E. Judging from the pump reading of 17 gallons. Tank is 18, I think.

 

a lot of people say to check your float in the tank and maybe replace it. I bought a new one and never replaced mine. When i fill her up, it reads full. When it shows empty i still have 1/4 - 1/2 tank... Mine is a gauge issue as when i hooked up my After market gauge which is set to read for ohms, it read half when i the original read 1/4. So just something to think about. Could be a gauge issue or a float issue based on what ive been told

 

Mine went right to full when I filled it up today. But the engine dies (runs out of gas) when it still says there is 1/4 tank. I wonder if on mine the line that goes down into the tank is corroded to the point where it does not pick up the gas at the bottom.

The problem for yours could be either mechanical or electrical.

Mechanical: Is it possible that the float on your sender arm is "waterlogged" some and is not floating all the way to the top? What happens if you manually force the sender arm all the way to the top position? Then does the gage read "full"? If you take the sender out, you probably will have to use a jumper clip to ground the sender housing to the frame.

Electrical: The sender is just a potentiometer and the fuel gage is displaying the voltage between the supply and the middle leg of the potentiometer, with the bottom leg being ground. (12V = full, 0V = empty, or something like that). If your gage is reading low, then I wonder if there is a problem with a voltage drop somewhere - most likely in the wiring or the sender itself? I don't know what the specs are, but I would compare the battery voltage to the supply voltage at the sender. If those agree, then I would guess the problem is not in the wiring. Then you could compare the rreturn (signal) voltage to the supply as well, at various fill levels.

I was just working on my sender gasket yesterday, and today I filled up to see if the leak was repaired. If you need me to, I could tell you the supply and signal voltages at the sender with a relatively full tank.

 

Alecs has some good thoughts there.


If, after checking everything mentioned you don't find a solution then I just read this as a possible other thing to try. Check out the final post in this thread.


https://www.ford-trucks.com/forums/3...-accuracy.html



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I'm betting your problem is your gauge regulator (B9MZ-10804C) I have had a half dozen Ford do that in the last 35+ years and it was always the regulator was the problem. Bought a 74 Supercab three months ago and it did the same thing (temp gauge also) and after replacing the regulator, now all the gauges are accurate.

 

I just replaced the sending unit in my truck after I broke the old one, how U say by adjusting on it.

After getting the new one in I didn't see much difference. I pulled the hot wire stuck it to the tank and the gauge went to full like it should.

I looked over at the ground connection an say huuuuumm. I pulled it brushed the hello out of it with one of those brass looking tooth brushes as well as some scraping with the pocket knife. It' seems to be working mucho better. I should have done that to begin with.


John

 

ICVR affects both the fuel and temp gauges. When it begins to fail, the needles of the fuel and temp gauges do "the hula" .. swing wildly back-forth on their own.

B9MZ-10804-C .. ICVR-Instrument Cluster Voltage Regulator (Motorcraft GR-510) / Obsolete ~ Available from auto parts stores.

Misc applications: 1961/66 F100/1100 / 1965/66 Mustang / 1966/77 Bronco.
--------------------------------------------------------------------------------------
The float is made from two pieces of copper soldered together. Solder breaks down, gas seeps in, float settles to the bottom of the tank.

COAZ-9202-B .. Fuel Tank Sending Unit Float / Available from Ford

Applications: ALL 1957/79 FoMoCo vehicles.

 

I usually fill my tank to 3/4.


This morning it was almost empty so I cruised into the station to put 10 gals in.


At 9.5 gals it spit gas at me.


Got in the truck and the gauge reads 3/4.


So now I have an inaccurate gauge as well.

 

For kicks & giggles give the ground wire a good scraping where it connects to the cab. That is too easy fix if that is where the problem is.


John