gas gauge fd up and i give up

[esty]

i've tried all the fixes talked about here that i could find plus any and all that i could think of

i've grounded 3 instrument cluster, install 4 sending units...run new wires from the dash to the tank...run additional ground wires from the sending unit and still no joy

help & thanks

[ray_]

Well, maybe it's the gauge.

Is it just pegging? What happens if you unplug the wiring to the gauge?

GL,

Ray

[1971Ginger]

Esty don't let it get the best of you I was just in the same situation turned out just a bad ground and it up grounding it to another wire try to do that run aground and touch different points around the steering column and whatnot.

also the wiring harness that plugs into that circular plug with multiple pins controls the gas gauge therefore if thats corroded or not connecting right we could have a faulty reading

[Koblenz]

Mine is either pegged on full or empty depending on how the wires are placed. I'm wondering if its the sending unit.

[BillWilliams]

Esty, will you gauge react to grounding a wire in the trunk?

Trying to figure out if your deal is the gauge, wiring or sender.

If the gauge reacts to grounding the wire, we may be able to rule out the gauge.

To test the sender, place an ohm meter on the two connectors on the sender and gently move the float up and down. If the ohm reading move, then we can rule out the sender.

One, of many, things I do not know is where the circuit gets its power.

Because as you know, the gauge is just a big ohm meter and even an ohm meter has to have power to work.

If I knew where this was, or how to test it, we could move to that test.

Sorry I am little short on that piece

[Mike Self]

To do it right, disconect the two wires (be sure and test to make sure the brown ground wire is really grounding somewhere) remove the sender unit from the tank and let it drain. Then remove the outer aluminum housing to expose the resistance wire and the float--be VERY careful as the wires and float are delicate. Now for some testing:

The resistance wire inside the unit is rated at about 6 ohms/inch. With the float at the bottom of its travel (empty tank), you should read maximum ohms--75 seems to stick in my mind. With the float at the top of its travel the ohmeter should read nearly no resistance.

If you have a good ground, get good readings as above, and the float isn't stuck, then the sender isn't the problem.

cheers

mike

[rms_sandiego]

Esty: Any progress on your fuel gauge? It may also be that the actual circuit board the instruments mount on has a crack at a lead. I had that occur on mine and found it by careful inspection. I was able to resolder at one point and created a jumper wire in another.

[Koblenz]

Update plesae.

I just ordered a new sending unit. After removing it from the tank I discovered the sleeve housing was no longer attached to the top half

[esty]

Update plesae.

I just ordered a new sending unit. After removing it from the tank I discovered the sleeve housing was no longer attached to the top half

i still don't have a clue & it's still broken...but i do know that i'm getting power from the brown/yellow wire to the sending unit...i noticed something unusual this afternoon when messing with it though....it still pegs to the full position when i turn on the ignition with the ground wire disconnected from the sending unit...

can anyone explain why that may be happening or how it's possible

[Guest Anonymous]

From the symptoms described sounds like a bad tank sensor. A full tank causes the float to rise which increases the resistance of the sender and causes the guage to read full. With a low tank the float is lower in the tank and the lower resistance will cause the gauage to read low. By removing the ground you've basically opened the circuit simulating a full tank and your guage read full. Now short both connectors at the tank sensor and you will simulate an empty tank and see if your guage reads low. You can also remove the tank sender and slide the float up and down to do the same

[jimk]

From the symptoms described sounds like a bad tank sensor. A full tank causes the float to rise which increases the resistance of the sender and causes the guage to read full. With a low tank the float is lower in the tank and the lower resistance will cause the gauage to read low. By removing the ground you've basically opened the circuit simulating a full tank and your guage read full. Now short both connectors at the tank sensor and you will simulate an empty tank and see if your guage reads low. You can also remove the tank sender and slide the float up and down to do the same

DareR, The resistance varies just the opposite. a full gank means a short resistance wire in the sender and a low resistance reading. The circuit in the sender is from ground thru one side wire, across the slider on the float and tru the opposite wire to the terminal.

When I got a longer one for the deeper tank, I took it apart and cleaned the wire and slider with a solvent. It was dirty and can affect the contact between the wires and the slider. I agree an open cireuit at the sender would show a full tank. The same with a temperature sender, hot.

My car had the open curcuit in the printed circuit board in the gauge pod in 1972 and the thermostat stuck before I had it figured out. I had my electrical engineer explain to me, a mechanical, how the gauges work.

[Swiftus]

nc

[bnam]

Update plesae.

I just ordered a new sending unit. After removing it from the tank I discovered the sleeve housing was no longer attached to the top half

i still don't have a clue & it's still broken...but i do know that i'm getting power from the brown/yellow wire to the sending unit...i noticed something unusual this afternoon when messing with it though....it still pegs to the full position when i turn on the ignition with the ground wire disconnected from the sending unit...

can anyone explain why that may be happening or how it's possible

My thoughts:

The Br-Ge wire is a switched ground wire -- with the tank sensor being the "variable switch" -- at full tank there is low resistance so it is fully grounded, draws the most amps and pegs the needle which needs the higher current to go to full scale reading. At low fuel levels, resistance is high, current is low, and gauge should read low. If you unplug the brown (ground) wire at the sensor, and the gauge still reads full, then that is not caused by a bad sensor unit.

One possibility is that the Br-Ge wire is grounding out somewhere allowing current to flow thru the gauge coil even when Br wire is unplugged at the sensor (which should have ungrounded the Br-Ge wire). You can test for that by disconnecting the round connector behind the instruments and then connecting an ohmmeter between one end of Br-Ge wire and the body. If there is no grounding, then you've isolated the problem to the instrument panel.

If the problem is in the gauge, I would look for a short or misire somewhere. My thought is that an open circuit would cut off the current flow and not move the needle, so I'd look for something that is allowing current flow thru the coil even when the Br-Ge wire is in open circuit.

BTW, I have a tested good sending unit (if your car is a non-Tii) I can loan you if you'd like to try it before you use the new one. If by sleeve housing you mean the plastic housing around the bottom part of the sensor, it is held on by a small nut at the bottom. Perhaps your existing sender can be repaired by replacing that (if it measures correctly on resistance reading).

Byas

[Koblenz]

Thanks everyone.

The one I removed was close to being in two pieces. The sleeve that houses the float was no longer attached to the base of the top plate where the wires are connected. I have already ordered a new one.

Thanks for all the great help. Esty, keep us posted. I will buy the beer when its over.