gas gauge woes

[Gunboat]

ok,seems like I am never going to stop working on this 92 z34...now the gas guage isn't reading right. It says a quarter of a tank of gas but it is empty...any ideas? I know that it's either the guage or the sending unit...I replaced the fuel pump last year and everything looked fine on that end...When I fill it up it goes way past the full .mark...thqks in advance...

[Nas Escobar]

Pull the needle and put it on E when it runs out of gas or fill it up and put it where you think it's acceptable to be when the tank is full. Not the best solution, but the needle itself may be out of sync. I feel this may be the case on mine. My needles are faded and the trip counter doesn't work. It rolls but I can't reset it.

[Gunboat]

thanks,thats a good idea!

[Gunboat]

that didn't work

[rich_e777]

Pull the needle and put it on E when it runs out of gas or fill it up and put it where you think it's acceptable to be when the tank is full. Not the best solution, but the needle itself may be out of sync. I feel this may be the case on mine. My needles are faded and the trip counter doesn't work. It rolls but I can't reset it.

 

That doesn't "feel" like a good fix. Seems to me the gauge is either stuck or receiving a signal to read a 1/4 of gas. Maybe the associated wiring harness between sending unit and gauge is damaged at some point. Or you have a bunch of crud in your tank that fouled up your semi-new fuel pump assembly.

[Schurkey]

The usual problem with gas gauges is neither the gauge nor the sending unit. (Of course, anything is possible.) The common problem is in the harness connecting the gauge to the sending unit, or the wire(s) grounding the sending unit. If the sending unit is grounded to the body, there has to be an appropriate cable connecting the body to battery negative.

 

If the wire from gauge to sending unit has an open circuit, the gauge reads past "Full". If that wire has high resistance but isn't actually open, the needle is farther "Full" than what would be accurate. (If the wire is grounded, the needle reads below "Empty".)

 

First Guess: Put the gauge needle back where it belongs, and fix the high resistance in your fuel gauge wiring. You're looking for corroded wire, corroded connections, or poor ground. An ohmmeter is your friend.

 

AFTER you've verified the wiring and connections, and if that doesn't fix the problem, you'd look into the sending unit--stuck float arm, defective contacts in the pivot/resistor assembly, etc. THEN deal with the guage itself.

 

I had a salvaged sending unit that I could plug into the wire harness. Then I'd move the float arm by hand and have someone watch the gauge. If I could get a proper range of needle motion using my sending unit, I knew that the wiring between gauge and sending unit was OK. Not everyone has a spare sending unit laying around.

Edited April 19, 2015 by Schurkey