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Join Date: Jul 2003
Location: Silicon Valley, California, USA
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Question Troubleshooting non-functional fuel guage

I did a quick search on how to troubleshoot a fuel guage but can't find what I need. My guage is near E but above the idiot light. I went to put gas in the car and the pump kept clicking off. I was about to blame the gas pump when I looked in the tank, it was full.

What I know:
The guage doesn't move when I turn on/off the ignition key. I pulled the sender out out of the tank and the float moves back and forth freely. I did not disassemble the sender itself. I polished the electrical connectors. My fuses are all good and clean. I studied the factory electrical diagram but it wasn't very helpful in this case.

Sender tests:
What resistance should I see when at empty and full?
There are three connections on the sender, ground, W and G. What's the W and G mean?

Guage tests:
Where can I apply power to the guage itself to see if its working?

Thanks in advance
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Rob
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'90 964 Cabrio - daily driver 220K miles
Old 02-14-2005, 03:27 PM
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Hi Rob
It's been about a year since I installed the tank back in my car so I'm going by memory here. I pulled the sender out of the tank and plugged the electrical connector on, then with the ignition on checked the fuel gauge operation by sliding the float up and down. When it completely bottoms-out it grounds a circuit (W) for the low fuel light. Seems the resistance ranges from near zero up to a hundred ohms or so. Put an ohmmeter across it (G) and see if the resistance varies linearly moving the float from one end to the other.
You might only have a bad connection at the sender or the back of the gauge, and verify you have 12V on the back of the gauge (red/wht wire).
Old 02-14-2005, 04:38 PM
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G == Gauge ; W == Warning light.

Resistance of the sender ("G" pin to ground) will be "around" 35 ohms when near empty, more like 5-10 ohms when full.

As Guy said, check the connections, then see what kind of resistance you're seeing from the sender.

--DD
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Old 02-15-2005, 01:12 PM
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The usual problem with sticky, jumpy, and non-responsive fuel tank level indications is caused by carbon build up on the resistive wire in the sender. The way to solve this is to remove the bottom mini-nut and remove the sender cover, thereafter carefully wipe the resistive wire down with fine steel wool to remove the minute debris stuck to it. This will result in the fuel indicator moving smoothy up and down, allowed by tke float smoothly moving up and down. The indicator only reflects what the float does.

Phil
Old 02-15-2005, 01:52 PM
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