Fuel guage haywire!? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 3 Old 03-05-2012, 11:04 PM Thread Starter
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Fuel guage haywire!?

OK so my fuel guage is stays above full..so i pulled the tank off today (while 3/4 of gas ) and pull my float unit out.I put a test light up to the wires that plug into it and got a very weak signal? anyhow , i could move the float by hand , turn the switch on and it would go to the appropriate spot where i had the float located (1/4 , 1/2 , full , and empty.).but only when id turn the switch off then back on would it reset to the new position i had moved the float to..so i installed the tank back and all and i was kinda hoping that the float was stuck previously or something but as soon as i hit the switch boom back above full..whats going on here? do i need a new float "unit" deal?? thanks

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'87 LX Mustang.H/C/I , Supercharged , geared.
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post #2 of 3 Old 03-06-2012, 03:24 PM
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Could be a short, but 99 times out of 100 it is the sending unit needs replaced.

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post #3 of 3 Old 03-18-2012, 09:18 AM
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maybe this will help with your trouble shooting

Originally Posted by 87coupe50 View Post
my understanding is that if you disconnect the harness at the sending unit and the gauge reads full then your sending unit is the problem, if the gauge doesn't move then its your anti slosh module.

My gauge wouldnt move at all, TODAY I tried to replace the sending unit and it still didn't work (before I found out about this trouble-shooting method). I found a couple anti-slosh modules at the junk yard (where I also found out there was a difference between 87-89 and 90-93), replaced it with a matching module and my gauge now works. There is also a write-up about swapping the large resistor (100 micro farad 25v) with one from radio shack.
also, the float arm slides across a resistor strip inside the sender. This strip gets worn out with use which is why most get a funky reading as the arm crosses over the worn out section or it doesn't read at all (except maybe totally full or empty). Resulting in the need for a new sending unit.

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Last edited by 87coupe50; 03-18-2012 at 09:24 AM.
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