Fuel gauge grounding

[M5Ivan]

I'm diagnosing my fuel gauge which never reads more than 3/8 full. By disconnecting and then grounding the wire at the gas tank (that leads to the gauge) it moves the gauge past the full mark. Does anybody know if this is supposed to read like this when grounded, or if it should only move the needle to the full mark? 

[Pete in NH]

Hi,

What you are seeing when you ground the fuel gauge wire and grounding it is normal. Don't leave this wire grounded too long you will damage the fuel gauge. Your test shows that either the fuel tank sending unit is bad or it is not getting a good ground. I'm pretty sure these sending units are grounded though the fuel lines and there should be a grounding strap/ clip on that goes across the short section of rubber fuel line between the tank unit and the steel fuel line running forward. It's been a very long time since I've been underneath a 2nd generation car.

[M5Ivan]

Hi,

What you are seeing when you ground the fuel gauge wire and grounding it is normal. Don't leave this wire grounded too long you will damage the fuel gauge. Your test shows that either the fuel tank sending unit is bad or it is not getting a good ground. I'm pretty sure these sending units are grounded though the fuel lines and there should be a grounding strap/ clip on that goes across the short section of rubber fuel line between the tank unit and the steel fuel line running forward. It's been a very long time since I've been underneath a 2nd generation car.

Thanks Pete! My car didn't have the ground strap but I've temporarily grounded it using alligator clips. This didn't change the reading, but since the gauge sometimes didn't register at all, I'm hoping the ground fixes that issue. I'm getting a 31 OHM reading off the sending unit which I believe indicates around 1/2 a tank which seems about right, but the gauge still reads just past 3/8ths. I guess I need to fill it up and check the readings again.

[rebby]

You're on the right track. If you ground the sending unit and don't see the resistance change, it's most likely not a ground problem. I'd lean toward the sending unit in that case. Repop sending units read differently than the old OEM units. Check out this thread for more information on that topic-> http://www.dodgecharger.com/forum/index.php/topic,123709.0.html