Gas Gauge Problems

[Gene Zick]

My wife and I were coming home from a car show. I stopped to gas up. The pump failed to shut off spilling gas all over my car. I cleaned it up and got home. The gas gauge was buried. When I shut the ignition off the gauge went right passed the full line. I checked all the wire connections, everything indicated okay. Next I removed the port where the float is at in the tank. I moved the float toward the bottom, gauge went to empty, pulled it to top went to full. I closed everything up and turned on key needle was passed full line returned to full. I shut off ignition and needle went back passed full again instead of returning to empty as it should. The float is less than1 year old, the fuel gauge was installed in 09. I have removed the seats and carpet to check all wiring and found nothing. Any ideas?

[Rick_L]

Gene, welcome to the site.

It's a small world, I spent my early life living in Greenville. Moved from there 50 years ago when I was early in high school.

On to your problem. I think you have a ground problem. Your ground was ok when you did your test and everything checked out. If your float was a problem it would show empty or near empty all the time (float doesn't float). When the tank is empty, you are at low/no resistance on the sender. When the tank is full, you are at the sender's maximum resistance (30 ohms). If your gauge shows over full, it's pegged, and that's because you've lost your ground connection between the tank and body, and the resistance is much greater than the sending unit's 30 ohms. I would suggest running a wire from one of the screw heads on the sending unit to the body. That way you don't have to rely on the tank itself grounding to the body. In fact I think there was originally a factory ground wire there (though it may not be there any more). Worst case, as a check, run a wire from the sending unit all the way to the negative post of the battery.

[chevynut]

Good catch Rick.

[Gene Zick]

There is a ground wire from the float to the body. I cleaned the connection, nothing. I ran a wire from the float to the ground on the battery. Still nothing. I double checked all the connections at the tank and at the instrument panel. Still goes past the full line when ignition is off and returns to full when the ignition is on. ??????

[56-210Sedan]

I bookmarked this information might be worth a try.

FUEL GAUGE Checklist with Ignition 'ON'.

Gauge pegs itself to the right, above full, some possibilities are:

Brown wire is off back of gauge.
Poor connection at underdash to tail lamp harness plug.
Brown wire is broken between gauge and sending unit.
Brown wire is off of the sending unit.
Bad tank to body ground.
Sending unit is bad.

[Rick_L]

I suppose it is possible that the sending unit wire (brown wire) has an intermittent open.

[Gene Zick]

By sending unit I guess you are talking about the float? I traced the wire from the tank thru the trunk and under the carpet to the fuel gauge. I found no breaks or frayed wired. Could the gauge just be bad. The chevy manual says it has to be in the grounding. The float was just removed and reinstalled in a new gas tank about 2 weeks ago, but the fuel gauge problem happened about a week before that. I double checked the ground wire from the float to the frame this morning. Nothing changed.

[Rick_L]

If the gauge in the instrument cluster is showing over full, that's what it should do if you lose the ground at the tank, or the sending unit wire, or if the sending unit is open. So that means that it's the tank ground, the wire from the unit to the gauge, or the sending unit in the tank.

[chevynut]

Next I removed the port where the float is at in the tank. I moved the float toward the bottom, gauge went to empty, pulled it to top went to full.

What was different when you did the above, versus when the float (sender) is in the tank? If the gauge works correctly with the sender out of the tank, that should give you a hint as to what is wrong. Was the wire to the gauge still connected to the sender? Did you ground the sender itself?

If it worked like you said above, there is nothing wrong with the float/sender. Like Rick said, your wire from the gauge to the sender is either broken, or the sender isn't grounded.

[Gene Zick]

Went thru the checklist;
Brown wire is connected to back of gauge.
Connection to tail light is okay.
Took out back seat, remioved carpet- no broken wire betwenn gauge and sending unit.
Sending unit is groundied to body with a seperate wire.
Sending unit is okay.
I haven't been able to trace down anything specific. I thought I found it at the gauge. When I touch connection at the back of gauge with a wrench the needle went to empty with ignition off. Turn key on gauge went to full, shut it off gauge stayed at full. When I touch dash behind gauge with wrench I can control gauge. I have not been able to trace a short. Could the post for the brown wire on back of the gauge have lost connection inside? Frustrated.

[chevynut]

Next I removed the port where the float is at in the tank. I moved the float toward the bottom, gauge went to empty, pulled it to top went to full.

So how come it worked okay when you did this? What specifically did you do to accomplish the above? If you could move the sender float and make the gauge work before, there's nothing wrong with the gauge. How did you determine the wire from the gauge to the sender is not broken?

Something doesn't make any sense in what you're doing.

[Gene Zick]

I did not move the sender float today. As I said I removed the carpet and back seat to trace the brown wire down. There are no breaks or marks on the wire. I pulled the intrument cluster to gain access to the back of the gauge. The wire nut was not real tight so I tightened it. I turned the key on the needle was at full. I switched the ignition off, gauge stayed at full. I put wrench on nut holding brown wire needle went to empty. Repeated several times. When ignition is on needle goes to full. When I shut off ignition it stays at full but when I put wrench on brown wire nut again it goes to empty. I checked ground at sending unit to frame. I checked the harness that has the tail lights, nothing loose there.

[Rick_L]

I assume you are talking about the connection at the gauge. Sounds like it has a connection problem internally there.

Just replace the gauge. They usually don't go bad so I wouldn't have a problem with a used one. There are instrument clusters cheap on Ebay, craigslist, and at swap meets. Or try the classified at one of the other tri5 sites.

[chevynut]

Rick, if it was the gauge, how did he get it to work with the float out of the tank? I still haven't heard a good explanation of what he specifically did to make that work correctly. I personally wouldn't replace anything until I found the problem...that's just me.

Here's what you said before:

"When the tank is empty, you are at low/no resistance on the sender. When the tank is full, you are at the sender's maximum resistance (30 ohms). If your gauge shows over full, it's pegged, and that's because you've lost your ground connection between the tank and body, and the resistance is much greater than the sending unit's 30 ohms."

So since his gauge goes past full, if what you say above is correct, the gauge is seeing an open.

I would GROUND the wire at the sender, and if that didn't work I would GROUND the sender side of the gauge. If neither of those actions make the gauge go to empty with the key on, the gauge is likely bad.

[Rick_L]

Cnut, the only thing I'm going on is what the current symptoms are, which seem to have changed.

One thing not addressed. Gene, you said you inspected the wire from the tank to the gauge. But how do you know it doesn't have an internal break in it without disturbing the insulation?