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Fuel guage

 
bumpme1
New User
Posts: 8
Joined: 08/13
Posted: 09/07/13 05:30 AM

Does anybody know why my fuel gauge will NOT return to the (E)when I turn the key off, it will go to full when I fill the tank and have the key on ????? Confused   1987 Mustang LX  

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waynep712222
User
Posts: 124
Joined: 03/13
Posted: 09/07/13 08:08 AM

fuel gauges are a strange beast..


they will come to a rest where they like when you turn off the power...

there is no spring to return them to zero position..


they are a dampened OHM meter sort of thing.

pulsed 5 volts gets to one side of the gauge...

the sending unit in the tank connected to the other..

the sending units have a range of 0 to 90 ohms..

so depending on how much resistance there is between the body of the car.. the amount of negative electrons the sending unit allows thru to the gauge.. changes the magnetic field that moves the gauge...

when you turn the key off.. it just sort of stays close..

there are several articles on gauges here in the tech or archives.. and could be in almost any of the over 30 magazines on this site..  on gauges and clusters..

there are 4 specific mustang sites here also..

gas gauge testing...  unplug the sending unit... gauge should swing all the way in one direction when you turn on the key...     short that wire to ground and it should swing in the other direction..  this tests the wiring between the tank and the gauge  including the gauge...

if it does not go to both ends as you perform the test.. there have been issues with not just the gauge. but with the printed circuit cluster not making proper contact to from the printed circuit to the gauge pins...  also with the back of the cluster of some years.. just crumbling into dust.. the only way to fix that is with a replacement housing...  

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bumpme1
New User
Posts: 8
Joined: 08/13
Posted: 09/07/13 05:40 PM

Thank you !! I will try that tomorrow !  

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bumpme1
New User
Posts: 8
Joined: 08/13
Posted: 09/07/13 05:40 PM

Thank you !! I will try that tomorrow !  

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