Fuel tank sender

[JohnBM]

I have been having fluctuating fuel gauge readings for sometime now , have taken out sender ( original) everything moves ok , a mate of mine said to try taking off the wire from the sender & earth it ,turn on ignition & the fuel gauge should read full , which it does . he’s not available at the moment ,what does this mean & how do I sort it . I can run another wire from one of the screws to a suitable earth point but how does that stop the gauge from reading full even though it’s, say half full . Could also be a problem under the dash . Any help would great . Cheers John .

[Dr_Terry]

I don't believe that is correct.

AFAIK if you ground the sender wire, the gauge should read zero. If you place a 30 ohm resistor to ground the gauge should read full.

If the sender is disconnected, the gauge will read full scale (i.e. past full).

Dr Terry

[JohnBM]

Thanks dr Terry . Well I disconnected the sender wire this morning & earthed it adjacent to the sender ,being only a short bit of wire & fuel gauge definitely indicates full. I’ve now run a earth wire from a sender screw to a rear light holder screw to earth it . Which then indicated quarter full on the gauge ,about what’s in the tank. Anyway obviously I’m no expert .LOL .I’ll wait for my mate to return & get his advice as well .thanks .John .

[Errol62]

Sounds like you proved the sender wasn’t getting a decent earth John. Now you have given it one you should find if you bypass it to the new earth, the gauge will read empty. Open circuit it and gauge reads over full.

From my experience a functioning sender should read around 33ohms when in the full position and 2 ohms or less empty.


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[JohnBM]

Thanks Errol 62 . For your info . I suppose to be realistic with the fuel sloshing around even with a baffle in the tank , the fuel gauge needle would move around a bit .

[my8thholden]

mine moves when on road , but settles when stopped..Vern

[ardiesse]

I'm going to complicate matters.

The fuel gauge itself can go "noisy".  I bench-tested a couple of gauges with a 15 ohm resistor in place of the sender, so the gauge read half-full, and the needle fluctuated.  Intrigued, I measured the voltage across the resistor.  It fluctuated.  I got out with an oscilloscope, and the 'scope trace showed noise, just like you get with a scratchy volume control.

I'm guessing this is what happens when moisture gets into the coils in the fuel gauge.

Rob

[JohnBM]

Thanks Rob .

[JohnBM]

Does anyone know if a original fuel tank sender can be refurbished? ie that it can opened up ,& recalibrated using a multimeter . one of the first replies to my initial question mentioned OHMS in terms of resistance , do the numbers ,33ohms in the full position & 2 ohms in the empty position (approximately) seem about right for our cars ? getting to the inside of the sender would only be necessary if there was a internal problem . Cheers , JOHN .

[Rod]

Try this John.

http://www.fbekholden.com/forum/viewtopic.php?p=69947#p69947

Cheers Rod

[JohnBM]

Thanks very much for that Rob , very informative from the original author. I have a good earth point now to the sender and I believe the gauge reading has improved since . If not I’ll go down the road shown in the link . Cheers , John .