Fuel guage problems

[Anders]

My fuel guage have worked since I bought my car. The temp still works, but it seems as the fuel donīt as it still shows empty tank after I filled her all the way up. I saw a tread or something around this not long ago, but canīt find it again.
Trying to see if there was any loose wires behind the dial plate today, or something else "easy to find" I noticed that when I turned my ignition key on, the temp guage moved to where it should be, and the fuel moved like half a millimeter ( donīt know what that is in inch, but itīs VERY little , showing it might not be totally dead. Any suggestions what I should do here?

[simplyconnected]

GROUND your tank! OMG Anders, gauge voltage is already reduced to 6-volts. After copper wires reach the tank, the return path depends on rusty straps and sheet metal.

Drill a hole for a small (8-32) stainless screw, lock washer and nut in the un-used corner of your tank. Cut a short #14 AWG copper wire and crimp a ring terminal on each end. Bolt to your frame using a stainless screw.

These pics came from nysquarebird58:



Marcello shows perfect examples to ground because he painted and sealed his tank. Everyone should do this for much better gauge readings. Don't forget to calibrate your gauge afterwards. - Dave

[Anders]

Soon midnight here, but Iīll do it right away! Back in half an hour if it worked

Edit: Iīm back. I now have the same wire fixed. Didnīt help a bit

[benfisher]

I posted a question similar to yours a couple of weeks ago.
I grounded my tank, sent my gauges out for rebuild and replaced my CVR with a solid state unit.
Everything works great now, unfortunately your problem seems to be a grounding issue and is probably going to be a pain to located. I would recommend using the flashlight battery test on the fuel gauge to see if the unit is functioning correctly before tearing things apart.Check the sending unit, also check the continuity of the wire from the sending unit to the dash.
Good luck, Ben.
p.s. Thanks to everyone for your help with my gauge issue.

[simplyconnected]

...Iīm back. I now have the same wire fixed. Didnīt help a bit

Troubleshoot it, Anders. Remove the wire from your float. What voltage is on that wire (to ground)? If you don't see power, go upstream to your fuel gauge and measure there. Both sides should show six volts (average) to ground.

The float sending unit is 'the load resistor'. When the float is low in the tank, resistance is high (like an open circuit).

When the float is high (full tank), resistance is low (like a short circuit to ground) which drives the fuel gauge movement to "F".

So... if your gauge is good (power on both sides), you can take the wire off your float and watch the gauge drop to "E". Or, ground the wire at the float and watch the guage go to "F".

[jopizz]

Could be as simple as your float having a pin hole leak and being filled with gas. As mentioned ground the wire first to check that the gauge is working.

[Anders]

Troubleshoot it, Anders. Remove the wire from your float. What voltage is on that wire (to ground)? If you don't see power, go upstream to your fuel gauge and measure there. Both sides should show six volts (average) to ground.

The float sending unit is 'the load resistor'. When the float is low in the tank, resistance is high (like an open circuit).

When the float is high (full tank), resistance is low (like a short circuit to ground) which drives the fuel gauge movement to "F".

So... if your gauge is good (power on both sides), you can take the wire off your float and watch the gauge drop to "E". Or, ground the wire at the float and watch the guage go to "F".

When I measure the connector on the float ( Yellow connector ) and the ground it moves back and forth between 6 and 7 volts.

[simplyconnected]

Good! When you ground that wire does the gauge needle go to "F"? If it does, John Jopizz is right, your problems are at the float. The good news is that you can repair or replace your float. - Dave

[Anders]

No, the needle is still on empty

Will wait for "expert" ( hopefully...) -help later this week. If ther is one single thing in life that I just donīt get, it is electric stuff...

[simplyconnected]

Fortunately Anders, there is a lot on this subject. The components are simple and so is the wiring.

From your description, you have voltage at the tank which proves two things; your voltage regulator is working, and your wiring is good. I suspect your gauge may be a little funky. It could be an electrical OR mechanical fault in the gauge. - Dave

[Anders]

I still hope for some ground problem then. Last year, it worked fine, but sometimes not, back and forth, so perhaps itīs "just" corrosion somewhere

[Anders]

As i have another fuel guage, ugly with bended pointers, i thought i put that on in and see what's happend. No difference at all. Moved like 1 mm from empty ( tank is full ), so i suppose that means My guages are ok at least. Shall I follow the yellow, the white or the green wire?...

[simplyconnected]

We're not out of the woods yet. Things aren't acting the way they should.

Let's start with power from your Key Switch (Acc terminal);
Black & Green feeds your voltage regulator

I don't like it but both sides of your voltage regulator are the same color (Black/Green). Feed side is constant +12, load side is intermittant (6-volts average)

From the regulator you feed the Fuel Gauge first, then on to the Temp Gauge.

STOP RIGHT THERE. The Red/White wire continues to the Float. You said when you ground the float, the gauge doesn't move. If the gauge is good and it is getting proper power, grounding the float should make the gauge go to "FULL".

To prove the Red/White wire is not broken, CAREFULLY ground the Red/White wire at the gauge. The meter should point to "FULL". If it does, your wire is broken between the meter and the Float. If the meter does not move, you may have a bad Dash Power Supply.

I am assuming both meters are not broken. You can prove them by applying six volts from four dry cells (torch batteries) in series. Hold the batteries on the gauge just long enough for the needle to go up to "FULL". - Dave

[jopizz]

I thing you mean the YELLOW wire to the float. The Red/White wire goes to the temp sender.

[simplyconnected]

Yes John, thanks. I was standing on my head when reading this diagram.
I do mean Yellow, and after re-reading the print I see that the power wire goes to the Temp gauge first, and then to the Fuel gauge.

So, carefully ground the Yellow wire at the Fuel gauge. Hopefully it will go to FULL.