Fuel gauge not working

[Charger1973]

 

Well I cant seem to get my fuel gauge to work.  I have it hooked to the tank.  When I pull the lead from the tank and put it to ground the gauge pegs out but when i hook it to the tank, I get nothing.  I have the metal line connected to ground, I even grounded it with a wire directly to a ground screw and still got nothing.  Is there anything else I can try? 

[y3chargerrt]

Time to order a sending unit.

[GeneralLeeTESH]

That is correct! A sending unit is a "bobber"-controlled variable resistor. It is acting just  like the volume control on an electric guitar or radio! By movement (by the gas) up and down, the bobber (Attached to a lever-arm) moves the fuel-soaked resistor up or down in resistance. This is the "variable-Ground" in the circuit. The voltage regulator (on the back of the instrument panel) received 12 Vdc and makes it pulsate +5 Vdc on and off rapidly. This provides electrical power (+5Vdc pulsation) to all Fuel, Oil and Temperature gages on the dsh. (these are basically miniature volt-meters).
When you "ground the sending unit to anything metal (ground DC) on the car-you provide a +5Vdc signal to the (Voltmeter) Fuel Gage. When testing the oil gage or Temp gage-their wires individually can be tested the same way. The Oil Sender is a variable pressure transducer (strain gage) and the Temperature sender is a variable resistor (varies with heat).
That's today's Instrumentation lesson brought to you by Boeing Flight Test Instrumentation-Seattle, WA.

[darrin75]

not to hijack the thread, but my gauge pegs to full and stays there.  Everything is grounded, so would this be caused by the sending unit in the tank to be grounded out, when its not suppose to be???

[Nacho-RT74]

not to hijack the thread, but my gauge pegs to full and stays there.  Everything is grounded, so would this be caused by the sending unit in the tank to be grounded out, when its not suppose to be???

maybe wire is peeled off and making chassis ground

[Nacho-RT74]

  Is there anything else I can try? 

Time to order a sending unit.

[Charger1973]

Time to order a sending unit.

Anyone know the cheapest place to get one?   

[Charger1973]

I do have a couple others in old tanks.  Is there a way to test them out of the car? 

[Nacho-RT74]

you can just ground the unit and plug the blue wire down the car, moving the floater you will get read or not on gauge.

[Charger1973]

you can just ground the unit and plug the blue wire down the car, moving the floater you will get read or not on gauge.

Thanks.  I was thinking that but wanted to be sure that was the right way to do it.  I think im going to wait for a warmer day though. 

[Plumcrazy]

not to hijack the thread, but my gauge pegs to full and stays there.  Everything is grounded, so would this be caused by the sending unit in the tank to be grounded out, when its not suppose to be???

If it's just a problem with the fuel gauge, unplug the wire from the sending unit and see if the gauge still pegs.   If it doesn't, you need a sending unit.   If it does, the wire to the sending unit is shorted to ground.

[Nacho-RT74]

you can just ground the unit and plug the blue wire down the car, moving the floater you will get read or not on gauge.

Thanks.  I was thinking that but wanted to be sure that was the right way to do it.  I think im going to wait for a warmer day though. 

you can also check for ohms tester on bench... Haynes manual states 60 to 75 Ohms emty and 0.5 to 0.8 ohms full

anyway I would check down the car too

[darrin75]

how hard is to remove the unit, without dropping the tank.  It looks like it could be done??maybe??  I am pretty sure the sending unit is messed up in the tank. so I am going to replace it.

[Nacho-RT74]

Pretty easy. I have done several times. In fact AS MURPHY'S LAW, when I'm trying to help here, NOW MINE WENT BAD on a vacations trip I had this week... reparaible, but DAMN!!!!

Brass point piece just come off from floater arm, inside the resistance coil case.

I think is time for a new one anyway. I have repaired it once already. I will do again for a while I find a new one. Not down here for sure.

Be sure tank is at least half empty when remove

[Charger1973]

That sucks man.  I havent done mine yet either.  Hopefully soon though, I hate not knowing how much gas I have!

[Nacho-RT74]

That sucks man.  I havent done mine yet either.  Hopefully soon though, I hate not knowing how much gas I have!

even worse when you are on a long ride

[Charger1973]

Then again with gas prices so high, maybe I dont want to know how fast its going.   

[Adrian]

I had the same problem on my 70. Carried out the usual tests, ended up removing the sender to find that the float was full of fuel. Swapped the float & it works a treat

[Brightyellow69rtse]

i mine was broke when i bought the car and 7 years later its still broke. i never ran outta gas either. i just put gas in it every few times i drive it no worries i figure i get about 100miles per tank anyway lol.............Mike

[AKcharger]

My gage at full shows only 1/2, always has since I installed it in 2003...is there a way to rig/adjust the sender? or does that mean the sender is bad? ( I read a LOT of aftermarket senders are junk)

[70 sublime]

Does the gauge go down as soon as you use some gas or does it only start moving lower when you get to the bottom 1/2 of tank ?

[AKcharger]

Does the gauge go down as soon as you use some gas or does it only start moving lower when you get to the bottom 1/2 of tank ?

No it's somewhat accurate, it moves with the the consumption of fuel. The gauge really sits a little more less than 2/3 when it's full and when it hits empty it still has about 3-4 gallons left...I always fuel up when it his "E" anyway just to be sure.

Kind of funny, I top the car off before I put in in storage every year and when I pick it up and drive it again I look at the gage and think "Someone stole my gas!"  then remember about the gage being off  

[70 sublime]

The gas gauge works with power going through a small wire that heats it up makes it bend and makes the needle move (more heat moves farther)
On the gas gauge itself there is a hole on the back at the end of the lever
There is a little tab that comes to a point you can see through the hole
Pry it left or right lets you set the top end on the gauge itself

You have to take the dash all apart to get to it though so it will depend on how much you really want to see it say full when it is full

You will not be very happy if you do all this and it still works the same but that is what it sounds like to me when the gauge moves all the time but never gets right to the top
See if anybody else has any ideas

[70 Charger RT]

It sound like the zero and span needs adjusting on the gauge.  Take the gauge out and calibrate it when connected to your sender and a power supply and the 5v pulse voltage limiter (on the bench).