[Shiny]

If there was a resistive short causing you to measure 4 ohms low at the gauge when the tank is half full, the short is a resistance in parallel that brings 35 ohms down to 31 ohms.

1/Rt = 1/R1 + 1/R2, or 1/31 = 1/35 + 1/Rshort

Rshort = 271 ohms

Unfortunately, the resistance of a short like this is still higher than the "full" value of ~90 ohms. That dashes hopes of using the gauge to detect the short by unplugging the sending unit.

What other circuits are shared by the fuse for the gauge? If the gauge was the only circuit on the fuse, you could measure current at the fuse box with and without the sending unit.... but I suspect there will be other loads on that same fuse to make this fruitless.

This is a tough one..

I guess if the short was stable, you could add 5 ohms (or whatever) in series with the sending unit and get your gauge to read correctly. The chances of a "stable" short like this sounds pretty slim though...

You need some smarter help diagnosing this one!

Mike

[Bill Hanlon]

Originally Posted by Shiny

I guess if the short was stable, you could add 5 ohms (or whatever) in series with the sending unit and get your gauge to read correctly.

Wouldn't work across the whole sweep of the gauge because the 5 ohms (or whatever) is a fixed amount while the float resistance varies. It would only fix the reading at one point on the gauge.

If the point that it "fixed" were at or near empty maybe that would be good enough. Worrying about the full reading usually isn't as nerve wracking as worrying about do I have enough gas to get to the next gas station.

[JLMounce]

Originally Posted by Bill Hanlon

Wouldn't work across the whole sweep of the gauge because the 5 ohms (or whatever) is a fixed amount while the float resistance varies. It would only fix the reading at one point on the gauge.

If the point that it "fixed" were at or near empty maybe that would be good enough. Worrying about the full reading usually isn't as nerve wracking as worrying about do I have enough gas to get to the next gas station.

Yeah that makes sense. My current situation is the best possible without accuracy. My gauge will show empty while I still have fuel to consume. I'm not in danger of running out as it is. It's annoying though for sure.