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Old 09-23-2023, 01:23 PM
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Post Gas gauge issue...

As my diner story mentions in the lounge section...the 70 4spd car seems to have a gas gauge issue. It reads full...almost too full if you know what I mean.

That should of made me check things...but I figured there must be enough gas...wrong.

I will add some fuel today to get her running...

Any suggestions on how to scope this out..?? Electrical things are not my strong suit.

-wilma
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Old 09-23-2023, 02:52 PM
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My experience has been, if it reads empty (and its not) then the sending wire is grounded. If it reads full or above the sending wire is open. Bad connection or broken wire. If you recently unplugged anything under the dash, look at those connections as well such as where the intermediate harness plugs into the dash harness.
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Old 09-23-2023, 03:46 PM
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When it reads full the fuel sender is resistor is open therefore infinite resistance so it reads full. Check the resistance of the sender directly first and if ok check the wiring from the sender to the guage.
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Old 09-23-2023, 06:40 PM
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Quote:
Originally Posted by Steve Shauger View Post
When it reads full the fuel sender is resistor is open therefore infinite resistance so it reads full. Check the resistance of the sender directly first and if ok check the wiring from the sender to the guage.
The GM senders operative Zero to Ninety Ohms full scale range.
0 ohms Empty
90 ohms Full

An Open or infinite resistance will drive the gage to the right way past full indication.

Servicing sheet attached.

I built a "Gage sender" simulator that can be temporary installed in place of the Gas tank sender to the Car wiring and drive the Gage while sitting in the drivers seat. The Same can be accomplished by using a Resistance Decade box, but this tool is plug and play.
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Old 09-23-2023, 11:34 PM
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Testing can also be accomplished shade-tree style with a known good gauge sender and jumper leads to the sender harness and ground, to either condemn or rule out the sender. Or, just ground the sender connection and see if it goes to empty.
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Old 09-27-2023, 11:31 AM
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I've found that the transmitting wire is grounded if it reads empty. The transmitting wire is open if full or higher. Misconnection or wirebreak. Check the intermediate harness-dash harness connections if you recently disconnected something beneath the dash.
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