Fuel Gauge Only Indicating Full

kuhndogs · 03-14-2009, 12:38 AM

I replaced my gas tank and sending unit and connected the ground to the frame. When I attached the wires to the fuel gauge the level went straight to full. No gas in the tank. Any suggestions?

**John Strenk** · 03-14-2009, 04:23 AM

Make sure the fuel gauge is grounded first. If it's not grounded then the regulator is not working and you may go to full on the gauge.

Check the links below.

nitor · 03-15-2009, 09:17 AM

I thought the fuel gauge wouldn't work at all if the regulator wasn't working? Mine's on empty with a full tank. I checked the gauge by grounding the pink wire ('S' terminal) and it went to full, so I am under the impression that the fuel gauge is working and I'm looking elsewhere for the problem. Am I wrong?

**mmerlina** · 03-15-2009, 10:23 AM

http://www.jeeptech.com/electrical/gauges/

Scroll down to Fuel and Temperature Gauges, and below that is the resistance specs on how full the gauge shows. Double check to see that all your wires and connections match what is posted here.

You can also click on that picture above the text and it'll show you where the jumper goes in the back of your speedo.. be sure to double check that too..

Good luck.

**Mike Romain** · 03-15-2009, 10:49 AM

Quote:

Originally Posted by nitor

I thought the fuel gauge wouldn't work at all if the regulator wasn't working? Mine's on empty with a full tank. I checked the gauge by grounding the pink wire ('S' terminal) and it went to full, so I am under the impression that the fuel gauge is working and I'm looking elsewhere for the problem. Am I wrong?

You are right. The sender's ground is a small wire bolted to the crossmember in front of the tank.

With no ground on the regulator inside the gauge, it gets 12 volts I think. It doesn't like 12 volts for very long either...

nitor · 03-15-2009, 02:10 PM

Here's my whole story on this so far. The tank is an aftermarket, bigger tank. The guy I bought the Jeep from said the tank and the sending unit are new and he doesn't remember having ever worked. So I can't live with no fuel gauge and this is what I am doing.

I put a test light on the 'I' terminal, it stays on bright and continuously. When I put the test light on the 'A' terminal, it stays on bright and continuously. When I touch the 'S' terminal with the test light, it is on all the time but less bright than the others. Then I unplugged the 'pink' wire going back to the sender right at the drivers door harness. I grounded the 'pink' wire there, the gauge went to full. So, here's what I did. I bought an old gauge cluster from a friend for about $10 and I used the gauges in this cluster and hooked up a fuel gauge externally. This tests my current gauges and it's easier to work with.

I took the fuel and temp gauges out of the cluster. I drilled a small hole in the side of that fuel gauge case and attached a ground wire. Then I took the strap from the 'A' terminal on the current temperature gauge (temp to fuel) off and attached a wire from the current temp to the external fuel gauge. Then I took the wires off of my current fuel gauge ('I' and 'S' terminals) and attached those to the external gauge. Now with the external gauge, I put the test light on the terminals and the 'I' terminal is continuously on and bright. The 'A' terminal flashes with a pulse. The 'S' terminal flashes with a pulse also. In addition, when the 'A' terminal is flashing with the test light touching, the gauge start to read something. Now, I don't know how much fuel is in my tank right now, but it reads about a quarter of a tank. When I remove the test light, the gauge goes to "E". Touch it again, it send a reading again. I don't know where to go now, any help?

**Mike Romain** · 03-15-2009, 02:52 PM

Quote:

Originally Posted by nitor

Here's my whole story on this so far.

You just need to read the sender via the pink wire with an ohm meter. Does it register or not?

**John Strenk** · 03-15-2009, 03:58 PM

Quote:

Originally Posted by nitor

Here's my whole story on this so far. The tank is an aftermarket, bigger tank. The guy I bought the Jeep from said the tank and the sending unit are new and he doesn't remember having ever worked. So I can't live with no fuel gauge and this is what I am doing.

I put a test light on the 'I' terminal, it stays on bright and continuously. When I put the test light on the 'A' terminal, it stays on bright and continuously. When I touch the 'S' terminal with the test light, it is on all the time but less bright than the others. Then I unplugged the 'pink' wire going back to the sender right at the drivers door harness. I grounded the 'pink' wire there, the gauge went to full. So, here's what I did. I bought an old gauge cluster from a friend for about $10 and I used the gauges in this cluster and hooked up a fuel gauge externally. This tests my current gauges and it's easier to work with.

I took the fuel and temp gauges out of the cluster. I drilled a small hole in the side of that fuel gauge case and attached a ground wire. Then I took the strap from the 'A' terminal on the current temperature gauge (temp to fuel) off and attached a wire from the current temp to the external fuel gauge. Then I took the wires off of my current fuel gauge ('I' and 'S' terminals) and attached those to the external gauge. Now with the external gauge, I put the test light on the terminals and the 'I' terminal is continuously on and bright. The 'A' terminal flashes with a pulse. The 'S' terminal flashes with a pulse also. In addition, when the 'A' terminal is flashing with the test light touching, the gauge start to read something. Now, I don't know how much fuel is in my tank right now, but it reads about a quarter of a tank. When I remove the test light, the gauge goes to "E". Touch it again, it send a reading again. I don't know where to go now, any help?

Very good so far.

Your "test gauges" seem to be working. The test light has a low resistance so it will cause the meter to move as it should. Sounds like the sending unit is not grounded or not working or the wire to the gauge is broken. Worst case is since the regulator wasn't working, it could of burnt out your sending unit.

As Mike says, check the resistance of the sending unit on the pink wire coming from the sending unit. then check the resistance right at the fuel tank. If you get a resistance reading at the tank but not at the sending unit then you have a broken wire.

nitor · 03-15-2009, 05:31 PM

I went up the street and filled up. Then I did the test again. The gauge only reads half full when the tank is full. Also, when the test light is on the 'S' terminal, every flash makes the needle move up. Of course this makes sense. I thought the current from the tank, the 'pink' wire was suppose to be a steady current, just less when the tank is full, and more when the tank gets empty.

nitor · 03-15-2009, 06:58 PM

Nothing coming from the sending unit. I was hoping I didn't have to drop the tank. I'll try to get the time tomorrow.

**John Strenk** · 03-16-2009, 04:10 AM

Nope, there current supplying the power ar just pulses. That's the regulator you see working. Longer pulses when cold or low voltage. Shorter pulses when hot or higher voltage.

**Mike Romain** · 03-16-2009, 07:44 AM

Quote:

Originally Posted by nitor

Nothing coming from the sending unit. I was hoping I didn't have to drop the tank. I'll try to get the time tomorrow.

The sending unit is only a variable ground, nothing comes from it. You just check it for resistance. It is common for the little ground wire back there to get broken or rot off.

nitor · 03-16-2009, 04:23 PM

I did check for resistance. There is none. Now I believe there is an issue with the sending unit. Ground or pink wire.