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Discussion Starter #1 (Edited)
GTV fuel gauge in cluster problem

Hi all,

I recently had my instrument cluster out and was playing around with a battery and test lamp looking to see how everything was working. In doing so I appear to have damaged the fuel gauge.

In sending current through the fuel gauge the needle now almost always reads empty although at least the red light works when fuel is low.

The needle will wobble around a bit indicating that it isn't stuck or jammed.

Ideas???
 

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To test the meter you should hook up 12 volts to the power and ground terminals and then a potentiometer of about 0 - 200 ohms between the input terminal and ground. Twist the potentiometer and the needle should drive up and down.
 

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Discussion Starter #3 (Edited)
Thanks Alfaparticle. I don't have a potentiometer but. . .I have finally got around to addressing this problem.

PROBLEM: fuel gauge almost always shows empty (even on a full tank) in my 105 GTV 2000 (1974) RHD;

I have done some tests and found the following with the ignition on:

Brown wire at tank = 9.57 volts;
Yellow/Black wire at tank = 12.37 volts;

Removed fuel tank sender from car and tested resistance for:

Yellow/Black wire terminal:
Resistance When Full = 5 ohms;
Resistance When Empty = 343 ohms;

Brown wire terminal:
Resistance When Full = no reading;
Resistance When Empty = 0.00 ohms;

Brown wire to battery ground triggers empty fuel warning light on dash;
Yellow/Black wire to battery ground moves fuel needle from empty to full;

Grounding top of full tank sender moves fuel needle from empty to ¾ full which seems about right for the amount of fuel in the tank.

CONCLUSION: petrol tank sender is not grounding correctly however the low fuel warning light would normally work OK with the caveat that it was a little inconsistent suggesting there is a ground connection of sorts but that it may be weak.

SOLUTION: I wired a ground to the top of the fuel tank sender.

OUTCOME: The fuel gauge now works correctly - typically the fuel gauge needle still wobbles around but not nearly as badly as it once had.

What confuses me about this is why would the petrol tank failed to ground to the chassis when this did not occur when I originally installed the fuel tank 5 years ago-what's changed? The only thing I did immediately prior to this problem occurring was remove the instrument cluster from the dash.

NOTE: there is a rubber gasket between the top of the fuel tank and the underside of the sender.
 

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Thanks Alfaparticle.

SOLUTION: I wired a ground to the top of the fuel tank sender.

What confuses me about this is why would the petrol tank failed to ground to the chassis when this did not occur when I originally installed the fuel tank 5 years ago-what's changed? The only thing I did immediately prior to this problem occurring was remove the instrument cluster from the dash.

NOTE: there is a rubber gasket between the top of the fuel tank and the underside of the sender.
I had the same problem with my GTV and a dedicated fuel sender ground wire solved it all.

The fuel sender is grounded thru the gas tank to the body. However there are lots of gaskets involved: fuel sender to tank and tank to body (yours might have disintegrated over time). So the ground goes thru the small fuel sender screws and then thru the screws that hold the gas tank to the body. These screws can and do rust thusly preventing adequate grounding over time.

I'm wondering if the fuel sender was grounding out thru the instrument panel somehow and when you removed it, the ersatz ground went away. Remember that electricity will take the path of least resistance ....
 

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Discussion Starter #5 (Edited)
You may be right, there are a lot of gaskets etc between the top of the sender and the chassis. I should revise my previous post and say that the fuel gauge needle does not wobble as much as it once did so maybe this fix is a good way to reduce (but not eliminate) fuel needle wobble.
 

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For me, I first figured it was an earth problem when the fuel gauge read correctly when pumping fuel...

Checking earths seems to be step #1 in just about any electrical fault for an Alfa.
 
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