Fuel Gauge Testing?

[Guest Thuff51]

Hello All,

Trying to diagnose the issue with my fuel gauge. I just cleaned the fuel tank, rebuilt fuel pump, installed new sending unit and I get no readings with the stock gauge. Is there a way to see if the gauge works with a tester by putting power to it at the tank location? Not crucial but would like to have a working fuel gauge.

[Eric W]

New sending unit - is this the one with the bulge in the tube, and it then requires a piece of hose to connect back to the original line on the frame?

If so, the original metal line was the ground for the level sender. When that gets separated from the level sender with hose, electrical ground to the sending unit is lost.

On mine, I put a worm clamp on the sender unit & worm clamp on the frame-mounted fuel tube with a jumper wire in between.

What car are you working on?

[TexasJohn55]

Did you have a ground wire from screw on sending unit mounting to the body or frame? The sending unit must be grounded. The sender wire to the guage uses the variable resistance to make the guage sweep, usually low resistance (low ohms at empty) and high ressistance at full.

The guage itself has a power supply terminal and the sender terminal. the wire that goes to tank completes the circuit to ground thru the variable resistor tank unit, therefore if the unit is not grounded, it cannot complete the circuit.

The sender wire may be brown and sometimes you can find a connector inside or near the trunk that you can unplug and test for voltage or ground it to test guage reaction.

Just guessing, you did not identify what you are working on. It is not a John Deere or Toro is it?

Edited May 5, 2014 by TexasJohn55 (see edit history)

[Guest Thuff51]

Sorry. I'm working on a 1951 Buick Special. There was no ground wire present when I removed the tank but it makes sense what Eric W mentioned. Is it as simple as hooking up a sending unit ground wire to the frame as I believe thats my issue?

[Guest shadetree77]

Yes. Eric is correct. I went through this when I put an electric pump on mine. I severed the metal fuel line right before it connected to the frame back by the tank. Little did I know that the sending unit on these cars use that metal line to ground themselves. I ran a wire from the metal line to a bolt on the frame. Problem solved. Also, if your car happens to be converted to 12 volts you will need a resistor inline before the gauge.

[buick5563]

If the gauge shows full when you turn the key on, it is a grounding issue. If it shows empty, either the wire to the gauge or the gauge itself is bad....

Or you don't have any gas

[Paul Falabella]

OK, so how do I differentiate between a bad sending unit and a bad gauge? Guage reads E empty with ign. on. Ohmeter in sender wire at trunk reads 20.3 at gauge, 19.5. Pink wire shows 12.9 volts. Tank is near full. Or am I going about this wrong? I took gauge out to clean face a may have done it wrong!

[TexasJohn55]

Paul, if you have access to the guage in the dash, it is easy. Remove the brown wire, guage should peg out. Ground the brown wire terminal and guage should read low, E or below. Providing you have 12v on the other terminal of course, key on.

20 ohm at sender sounds more like empty range that full, full should read higher, like 60 or 70 maybe, I don't know exactly.

Edited May 29, 2014 by TexasJohn55 (see edit history)