Trouble with Fuel Gauge

[GT350Mike]

When the ignition switch is turned on, the fuel gauge indicator will sweep from empty to fuel, then return to empty. My initial thought was either improper ground to the gauge or the sending unit but after trying a few things to include running a jumper wire off of the battery straight to the gauge and sending, nothing changed. Any ideas/suggestions?

[Tommy]

If you know what resistance the sending unit should provide (e.g., 0-30 ohms), disconnect the wires at the sender and test the resistance across the two posts with a multimeter. If it reads about what it should for that amount of gas, then the problem is either the gauge or the wiring between the gauge and the tank. Otherwise, its the sender.

[dallas_]

Has it ever worked properly?

If not, some gauges need to be calibrated. You might want to check that.
If that's the case, you should be able to find instructions for your particular gauge on the manufacturer's website.

[GT350Mike]

The car has a few test miles and the fuel gauge has never worked. I think the sending unit is bad because I just checked the resistance and nothing registered on the ohm meter. I also check the gauge with the wires disconnected from the sending unit and it didn't move when the ignition was turned on which makes no sense to me.

Any other ideas before I commit to replacing the sending unit?

Edit: Here is a pick of the sending unit. If I have to replace it, can anyone identify the manufacturer?

[strictlypersonl]

That gauge has similar internal electronics to a Stewart-Warner. You can test its function quite easily. Download the ERA troubleshooting guide here:
http://www.erareplicas.com/427man/wiring/wprimer.pdf *fixed link Must be the internet's fault. ;>D

[DonC]

Bob:
Bad link. You left the L out of erareplicas. Should be http://www.erareplicas.com/427man/wiring/wprimer.pdf
Sometimes new employees get the name wrong );-)

DonC

[redmt]

If you replace either the gauge or the sender, replace them both an make sure they are a matched set. I played back and forth with gauge/sender ping-pong until I finally replaced them both as a set and haven't had any problems since.

[GT350Mike]

Don, Thanks for taking care of the link.

I talked with Tony and he said it might be covered under warranty but because SAI is under new management, I'll have to wait until Monday for a decision. Considering the car only 6-8 test runs, I hope they honor the warranty.

[Gaz64]

Mike,

There's no wire on the terminal marked "send" in your pic, only "Neg" is connected.

Is this pic with the sender wire off?

[GT350Mike]

Gary, by the time I took the pic I had already disconnected both wires. The sender is a three wire unit, left post is positive, center is gnd, and the right post is the send.

[Gaz64]

Mike,

The resistance of the sender should read 240 ohms empty, 33 ohms full.

The gauge will read nothing when the sender circuit is open, ie: faulty sender or wire disconnected etc.

I use a decade resistance box for gauge operation diagnosis. Quite easy to dial up your resistance values to test gauge operation in almost infinite steps.

[GT350Mike]

Originally Posted by Gaz64

Mike,

The resistance of the sender should read 240 ohms empty, 33 ohms full.

The gauge will read nothing when the sender circuit is open, ie: faulty sender or wire disconnected etc.

I use a decade resistance box for gauge operation diagnosis. Quite easy to dial up your resistance values to test gauge operation in almost infinite steps.

Thanks Gary. SAI stated the same about the ohms reading. At the moment, they will not warrant the sending unit so before I call SAI to revisit my request to replace the unit, I'm going to re-check the gauge, wiring and sender. The last thing I want to do is through parts at it, regardless of who's paying for it. Besides, the task of replacing the unit will be a major PITA!