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Fuel gauge always showing empty - tried everything; stuck

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karlovac

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Discussion starter · #1 ·
My fuel gauge has been reading empty for a few months. I've researched the causes online, and tried a variety of things, and I'm still stumpted. Here's what I've tried:

  1. Bridging the two terminals on the fuel pump connector (that go to the fuel level sender), to try to trick it into thinking that the tank is full. (I bridged A and B in the photo below).
  2. Measuring the resistance at the fuel level sender terminals. (Between C and D in the photo below, which was infinite).
  3. Measuring voltage at the fuel level sender terminals, coming from the cluster. (A and B in the photo below; it was 4.59V).
  4. New instrument cluster (temporary).
  5. Removing/reinstalling the existing fuel pump (in case the float was stuck).

Image


So I really don't know what to do next. #1 seems to rule out the fuel pump sender, unless I misunderstand how it's supposed to work. #3 seems to rule out a cut wire, since there *is* voltage running through that line. I don't know whether it's supposed to be 12v or ~5v. I think the electronics run on 5v but I'm not sure - anyone know?

The instrument cluster I put in temporarily (#4) seems to rule out a bad gauge.
 
#2 ·
You are only concerned with the two middle terminals.
If you are measuring infinite ohms on the tank side... then that's the issue. The float sensor should be giving you a value between a specific resistance range.
That range is something like 40Ω to 220Ω. (I don't know the exact value..... that info is not with me at this time.)

The cluster only responds to values in that range. so, shorting out the terminals will send 0Ω, and thus the cluster will not respond.
What you need to do first is... get a 100Ω resistor. Or something from 56Ω to 180Ω. Anyhting in that range should work.
Take that resistor and connect it across the terminals that feed back to the cluster. Turn the key on... and the needle should move.

If it does... then I would say your float is pooched.
Although... as I first said.
You should be reading a resistance value from the tank sside connector. Even if the it's totally full or bone dry empty.
 
Discussion starter · #6 ·
I just wanted to close the loop on this, since I installed a new fuel level sender today. It definitely was bad; the fuel gauge works now. Here's a picture of the old unit, and you can see the hairline wire that's broken:

Image


I'd missed that when I took the sending unit out earlier while troubleshooting.

Thanks for all your help!
 
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karlovac
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