Fuel gauge sender

[L.C.Gray]

My fuel gauge isn't working, stays on 1/8 tank whenever the keys on. I'm suspecting the sender float is bad. How hard is it to access the sending unit? Do you have to drop the tank?

 

[72HCODE]

no you will not need to drop the fuel tank. in fact you may not need to even jack up the car.

you will need to drain the tank down as much as you can before you open the sender seal.

on the drivers side of the car on the lower part of the fuel tank you will see the connector plug for the sender and the fuel line.

pop off the connector clean it if needed as it is exposed to water and gets corroded.

pop the fuel line, finish draining any gas that may come out.

you will see the seal ring for the sender. pop that with a large flat head screw driver, a couple of taps on the ears of the ring should open it. turn counterclockwise from what i remember,

the ring comes off and you can pull the sender out with the float.

there will be a rubber o-ring as well watch for it that is the seal for the sender. make sure the sock is on the end of the sender it can fall off inside the tank.

now is a good time to shine a flashlight inside and look at the condition of the inside of the tank and if you see debris inside. if it looks bad inside with rust and huge chunks then i would change the tank as well.

then you can replace the sender and re-assemble. put some vasoline on the new oring seal. the reproduction sender used to come with a new ring and seal. once back together you will need to test calibration. this can be frustrating.

you fill the tank with 5 gallons of gas and the gauge should read about 1/4 tank.

if it doesn't you need to take everything apart again and bend the float arm a little put it back together and retest, then you repeat this until you get the reading you want.

you might want to test the new sender before doing anything, either use a ohm meter or plug in the sender touch the body with it and move the lever and see if the gauge moves with the sender connector plugged in.

my gauge reads low about 3-4 gallons, i didn't care to take everything apart over and over trying to get it perfect.

 

[Jeff73Mach1]

Before you pull the sender clean everything and test resistance with an ohm meter. It might just be dirty and loose connections. On level ground you can remove it with about 4 gallons of gas in the tank. If you have a little more, just jack up the driver side and put it on jack stands. I did mine this way and had the driver side raised almost as high as my jack would permit.

 

[c9zx]

Briefly ground the yellow/white stripe wire at the sender with the key on to see if the fuel gauge moves upscale. If it does, the gauge is good and the sender is the problem. If it doesn't move upscale, measure resistance from the pin on the sender to a known good ground. It should read less than about 80 ohms. If it reads infinite resistance the sender is bad. If it reads less than 80 ohms, check for voltage on the yellow/white stripe wire. if there is no voltage, it is a wiring or instrument constant voltage regulator problem. Let us know what you find, it helps everyone. Chuck

 

[L.C.Gray]

I did a test by unplugging the fuel sender and running a jumper between the two terminals in the plug. With the ignition on my fuel gauge read full. This is telling me the issue is with the sender and not the dash gauge. As I read the catalogue I take it some models had a low fuel light? How do I know if mine does or not?

 

[72HCODE]

Your connector would have 3 contacts instead of 2 posts. You would also see a light for low fuel on the gauge.

 

[midlife]

Your connector would have 3 contacts instead of 2 posts. You would also see a light for low fuel on the gauge.

There may be three pins on the connector going to the fuel sending unit, but only a few cars had the low fuel line active. For that to happen, there would be three separate wires going to the plug. In all of the 100 or so 7123 tail-light harnesses I've examined, I have yet to see a low fuel line.

To the OP: Yes, the problem seems to be in the sending unit.

 

[L.C.Gray]

Thanks for the input. I ordered a new stainless fuel sender assembly with brass float tonight.

 

[L.C.Gray]

Mission Success!!!

I think the old sender has seen better days....

 

[72HCODE]

and the float is missing!

ah,, look inside the tank with a flash light and maybe a mirror. if you spot the float try and get it out somehow.

its a round cylinder looking thing that is suppose to float. it used to snap into the end of the arm where the U shape is.

since the float is gone that would explain why the gauge read 1/8" most likely the pivot arm is all gummed up with rust also.

 

[L.C.Gray]

My guess is float was plastic, disentigrated years ago and is already out the tailpipe.

I didn't look in the tank.... some things you're just better off not knowing about...

 

[72HCODE]

in addition to the new sender with new filter, install a external fuel filter .

 

[Jeff73Mach1]

If the sender is that rusty, I believe the inside of your tank is probably in similarly poor condition. A new tank is cheap comparatively speaking and not having rust in your fuel lines is priceless.

 

[nbracken]

Thanks for the input. I ordered a new stainless fuel sender assembly with brass float tonight.

I just did this exact same job - it is a pain in the a**e but quite straightforward.

A couple of tips from my recent experience.

- the first new sender i bought from NPD had the outlet pipe set at 90 degrees to the rear - i.e. wrong! When I returned they checked and all others were the same. They then said they had another part 'with an improved design' (!) that was a touch more expensive but had the outlet pipe at the correct angle

- the new sealing O ring is a shade small and you need the Vaseline to make sure it stays in the correct position when fitting. On my first fitting I obviously didn't get it quite right and I had a small leak that of course only became apparent when I had some gallons of fuel in....so I had to do the whole draining procedure again. Second time it went fine.

- I have not yet done the calibration properly but must do that. When full I now read 3/4 full. One for the winter! In hindsight I should have done it at the time but wanted my car for Woodward and Mustang Memories in August.

 

[jbojo]

I just did this exact same job - it is a pain in the a**e but quite straightforward.

A couple of tips from my recent experience.

- the first new sender i bought from NPD had the outlet pipe set at 90 degrees to the rear - i.e. wrong! When I returned they checked and all others were the same. They then said they had another part 'with an improved design' (!) that was a touch more expensive but had the outlet pipe at the correct angle

- the new sealing O ring is a shade small and you need the Vaseline to make sure it stays in the correct position when fitting. On my first fitting I obviously didn't get it quite right and I had a small leak that of course only became apparent when I had some gallons of fuel in....so I had to do the whole draining procedure again. Second time it went fine.

- I have not yet done the calibration properly but must do that. When full I now read 3/4 full. One for the winter! In hindsight I should have done it at the time but wanted my car for Woodward and Mustang Memories in August.

I did the same and did not do the adjustment to the sender so my gauge is off too. Instead of pulling it since the sender varies the resistance depending on fuel level I am going to try to add a resistor in parallel to compensate for the error and that should fix it. Just don't want to drain the tank again. If the fuel gauge is reading less than what's in the tank you need to add a resistor in parallel to the sender and if it's reading more then you need to add it in series.

 

[Jeff73Mach1]

I drain my tank by driving! I put mine in without any calibration, just made sure it sat so that the arm was sitting roughly perpendicular to the tank side seam. Turned out that full and empty look like they are about equally above and below the markings.