Fuel Gauge question

[Jeff73Mach1]

I have a fuel gauge issue. The ground stud has popped off the sending unit.

I have the wire grounded to the tank with an alligator clip for the time being, and it works, but fluctuates a lot while driving. I think if I ground to chassis it will be better as the tank is painted and is probably not well grounded itself.

Am I correct that the stud is just a ground and any ground will work?

 

[rvrtrash]

I have a fuel gauge issue. The ground stud has popped off the sending unit.

I have the wire grounded to the tank with an alligator clip for the time being, and it works, but fluctuates a lot while driving. I think if I ground to chassis it will be better as the tank is painted and is probably not well grounded itself.

Am I correct that the stud is just a ground and any ground will work?

If you want the gauge to be accurate, you'll need to repair or replace your sender. The further away you place the ground, the worse it will be. The gauge is reading the resistance across the sender (which is why both wires hook to the sender) and if you add the resistance of the sender mounting, gas tank mounting ("painted and is probably not well grounded itself"), etc. by grounding to the frame, it may not even work at all.

Steve

 

[jbojo]

I have a fuel gauge issue. The ground stud has popped off the sending unit.

I have the wire grounded to the tank with an alligator clip for the time being, and it works, but fluctuates a lot while driving. I think if I ground to chassis it will be better as the tank is painted and is probably not well grounded itself.

Am I correct that the stud is just a ground and any ground will work?

If you want the gauge to be accurate, you'll need to repair or replace your sender. The further away you place the ground, the worse it will be. The gauge is reading the resistance across the sender (which is why both wires hook to the sender) and if you add the resistance of the sender mounting, gas tank mounting ("painted and is probably not well grounded itself"), etc. by grounding to the frame, it may not even work at all.

Steve

+1

Jeff,

I think that you are going to have to replace/repair the sender. The fuel float is a variable resistor from about 10 ohms (Full) to 83 ohms (empty) resistance and if you connect to a good ground I believe that it will always indicate full doing it the way you describe. I could be wrong but that's the way the electrical schematics indicate. I think that you are getting a reading other than full right now is because you do not have a good ground right now. A quick check to verify this is hook it to a good ground and see what the gauge indicates. I am guessing it will be full. Take this with a grain of salt as I have not actually tried this.

-john

 

[Jeff73Mach1]

Okay, I suspected this might be the case. I'll try and see if I can make a repair on the sending unit without pulling it. If not, I guess I need to burn 15 gallons of gas. That should take about 15 minutes of spirited mayhem.

Gauge read 1/4 full when I hooked it up. I had put in 5 Gallons Saturday after a test drive and then went to 7/8 full after I added 10 gallons, so I know I am close-

 

[c9zx]

Okay, I suspected this might be the case. I'll try and see if I can make a repair on the sending unit without pulling it. If not, I guess I need to burn 15 gallons of gas. That should take about 15 minutes of spirited mayhem.

Gauge read 1/4 full when I hooked it up. I had put in 5 Gallons Saturday after a test drive and then went to 7/8 full after I added 10 gallons, so I know I am close-

Siphon pump and gas cans worked for me. Chuck

 

[jbojo]

Okay, I suspected this might be the case. I'll try and see if I can make a repair on the sending unit without pulling it. If not, I guess I need to burn 15 gallons of gas. That should take about 15 minutes of spirited mayhem.

Gauge read 1/4 full when I hooked it up. I had put in 5 Gallons Saturday after a test drive and then went to 7/8 full after I added 10 gallons, so I know I am close-

Just a thought here. When you do get a new sending unit try measuring the resistance before installing it. I have heard that some of these units have resistances that are way off so you don't get accurate readings with the new one. If the resistance falls between the 10 to 83 ohm range when the float goes through the full travel it sound be good. 38 - 40 ohms should indicate a half tank.

 

[Jeff73Mach1]

I don't intend to replace the sender. I can repair it. I have a welder

 

[jbojo]

I don't intend to replace the sender. I can repair it. I have a welder

Cool, let me know how it goes.

 

[midlife]

I have a fuel gauge issue. The ground stud has popped off the sending unit.

I have the wire grounded to the tank with an alligator clip for the time being, and it works, but fluctuates a lot while driving. I think if I ground to chassis it will be better as the tank is painted and is probably not well grounded itself.

Am I correct that the stud is just a ground and any ground will work?

If you want the gauge to be accurate, you'll need to repair or replace your sender. The further away you place the ground, the worse it will be. The gauge is reading the resistance across the sender (which is why both wires hook to the sender) and if you add the resistance of the sender mounting, gas tank mounting ("painted and is probably not well grounded itself"), etc. by grounding to the frame, it may not even work at all.

Steve

+1

Jeff,

I think that you are going to have to replace/repair the sender. The fuel float is a variable resistor from about 10 ohms (Full) to 83 ohms (empty) resistance and if you connect to a good ground I believe that it will always indicate full doing it the way you describe. I could be wrong but that's the way the electrical schematics indicate. I think that you are getting a reading other than full right now is because you do not have a good ground right now. A quick check to verify this is hook it to a good ground and see what the gauge indicates. I am guessing it will be full. Take this with a grain of salt as I have not actually tried this.

-john

I don't think so. The ground lug on the sending unit gets its signal from a ground ring on the tail-light harness, which screws into the chassis. Using a gator clip (from U. Florida, of course!) to a good chassis ground will do just fine.

As for welding a new stud on, please make it a video. Several of us would like to see it!

 

[Totalled]

10-73 ohm.

 

[rvrtrash]

I don't think so. The ground lug on the sending unit gets its signal from a ground ring on the tail-light harness, which screws into the chassis. Using a gator clip (from U. Florida, of course!) to a good chassis ground will do just fine.

As for welding a new stud on, please make it a video. Several of us would like to see it!

I would like to clarify, as I believe there is some confusion, probably on my part. I was under the impression we were talking about running a wire from the ground side of the female plug in the harness to the frame, instead of clipping to the tank. That would require the sender to ground out through the locking ring to tank to tank straps to the body/frame. You're right in that the ground wire in the plug goes to chassis ground, and you can duplicate that ground on the chassis anywhere, but clipping to anything other than the ground stud of the sender for the other end of the wire is not an equivalent circuit. There is resistance from corrosion, coatings (galvanizing, paint, etc.) between the sender and the lock ring and between the lock ring and the tank and probably between the alligator clip and the tank or lock ring, wherever it's attached. Any increase in resistance is going to change the current flow through the gauge, giving a false reading, or possibly no reading. You may also have fluctuations caused by the alligator clip vibrating or the clip may fall off completely. This is why it's important that the ground be sourced from the terminal on the sender itself. Hope this all makes sense.

Steve

 

[Jeff73Mach1]

First off

The alligator clip was a temporary expediant to determine what will work. When I determine where the best location for the ground is, I'll convert to a more positive design.

Yes it is from Florida. I am a Alabama alumni and I beat up a Florida Alumni to take the clip (which is why I have nearly 50 of them

I'll be glad to video myself welding on a gas tank full of gas. I will however require some cash donations before hand just in case. In the meantime I was actually considering using Elecritally Conductive Epoxy. Now that Midlife has spoken (Thanks man!) I'll probably just punch a hole in the tank flange and ground it there.

 

[midlife]

Shucks...just punch a hole in the tank itself and use a quality screw. Should work...