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Post Info TOPIC: Fuel gauge/sender. Quick diagnosis please.


Canadian Poncho Superstar!

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Fuel gauge/sender. Quick diagnosis please.


New sender in the 67.

Gauge reads empty ign on, tank near full. Unplugging it in the trunk (sender feed), the gauge quickly swings up and way past the full mark.

 

What's up? Any ideas?

 



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


A Poncho Legend!

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It has all the makings of a bad sender? Your circuit all the way up to tank is good according to the way past full when it's unplugged.

Was it new just now, or new as in last year maybe? Just wondering if you tested the sender before installing it?

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1966 Strato Chief 2 door, 427 4 speed, 45,000 original miles 

1966 Grande Parisienne, 396 1 of 23 factory air cars (now converted to a "factory" 4 speed)



Canadian Poncho Superstar!

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Sending unit should read either 0 or 90 ohms, I can't remember which one is full and which is empty.

 

What reading do you have from the sending unit with a full tank?  Measured where it connects to the the tail light harness by the trunk latch.





-- Edited by seventy2plus2 on Tuesday 28th of May 2024 06:55:37 PM

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70 2+2 convertible
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72 GMC Sierra

 

 



Canadian Poncho Superstar!

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I see about .2 ohms Clint.

Any it was a new sender Carl...but not tested.

I just hooked up a old and proven sender to the gauge ground (Brown wire from gauge in trunk at latch), and grounded the sender to body. Turned the ignition on and I can watch the gauge move while moving the float up and down. So I at least know the gauge and the circuit to it is good.

Disconnecting the brown wire to my simulation sender (open circuit), the gauge races up and past full. Just like the one in tank when disconnected. So I'm assuming there is at least a continuity down to my new sender.

Its almost like the new sender float leaked, has fallen off or the mechanism is stuck or jammed on empty.

 

A poor ground (increased resistance) would only cause the needle to rise, no ground, it would go past full. 0 ohms at empty, 90 at full.

 

Next. Attempt to raise the float through the filler and see if the gauge moves.

Regardless, the tank probably has to come down again.

 

Bummer. It's no fun dropping a tank, especially when it's full. Again...

 



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


Canadian Poncho Superstar!

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The thought just occurred to me that the brown wire as it is strung across the tank to the sender post...could be pinched by the tank, or is shorted to ground somewhere.

No resistance would set the gauge at empty as GM designed.



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


Canadian Poncho Superstar!

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Good diagnosis Mark. The wire should sit in an indentation on the top of the tank, often held by a couple pieces of tape. It should be halfway protected, but you know how that goes.

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70 2+2 convertible
70 2+2 hardtop
70 Parisienne hardtop
72 GMC Sierra

 

 

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