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MG MGA - Fuel gauge issue.

Hi all.
I recently ran out of petrol in my Coupe. The gauge has always worked reasonable well and the needles drops to zero when low fuel. However now the gauge to fill when full but only drops to half full when empty. When I remove the wire from the tank sender the gauge goes to full.
Any ideas? I really don't want to remove the sender as I have only recently got it stay dry.
s page

In case you haven't seen it, Barneys site has a good deal of comprehensive information on the fuel gauge. You will see that you can test the gauge easily enough, independent of the sender, so that you will then know if its the gauge or the sender is at fault.
Graham V

Link to Barney's site on fuel gauge calibration.

http://mgaguru.com/mgtech/electric/fg_10.htm

Mick
M F Anderson

I have the same problem and this is my task for today too.

Check the bullet connector under the starter switch. Clean this up if it is dirty and the resistance will decrease. Also check that the contacts at the back of the gauge are secure and clean for the same reason.

I have to check the sender connection too as it is ten years or so since I touched this


Dominic Clancy

If your sender unit has gone faulty and you decide to buy a new one, make sure that check its resistance range. It should be 0 to 70 ohms but you may well find that it is slightly different to this.

My original sender unit had a range of 15 to 98 ohms and although the gauge did move to the full position when the tank was full, it never dropped below 1/4 even if the tank was empty.
I more recently bought a replacement sender unit which had a much more accurate range of 0.5 to 72 ohms.
However, the gauge is really sensitive to voltage and so, although the needle range was much better, it still never dropped below 1/8th full and so you were still not sure how low your fuel level really was.

So, after a couple of breakdowns due to running out of fuel, I decided to do something about it.
Barneys Gauge-tech procedure for calibrating the gauge looked am little daunting and so I decided to fit the "Gauge-Wizard" by Spyder.

This electronic gadget lets you adjust the gauge needle positions so that it shows full when you fill the tank and empty when it actually is empty. It also has the brilliant option of a low-fuel light which comes on when you have a 1/4 tank full (2 1/2 gallons) and then begins to flash when the level drops to 1/8th full (1 1/4 gallons). Also you can electronically damp the needle movement so that the movement of the fuel in the tank doesn't cause rapid movements of the gauge needle.

It has proved to be absolutely spot on, particularly at low fuel levels where it really matters.

I know that Barney is not a fan of electronics on an MGA but, so far it it has been absolutely brilliant.

This is a link to an earlier thread about the Gauge-Wizard.

https://mg-cars.org.uk/cgi-bin/or17?runprog=mgbbs&access=&mode=archiveth&subject=6&subjectar=6&thread=2018071322574923959

Cheers
Colyn
It is

Colyn Firth

Last time I had this issue there was a piece of plastic hose in the tank stopping the foat from dropping--someone had left it there from syphoning the fuel out
William Revit

My only advice would be to not let this project get overly complicated. The mechanism and "electronics" (electronics might a bit of an over statement) are pretty unsophisticated. When my gasket was leaking around the sender, I pulled the pieces off the tank to replace the gasket and noticed the "float" was in pretty poor condition. Wanting to use the car that weekend, I made a gasket from a piece of deer hide and used a plastic wine cork for a float. Put it back together and it worked fine. That was almost 20 years ago. Everything still functions as it should.
Bill Haglan

Well done Bill!
Art Pearse

Would this work as a test(?), if I've got it right(?) -
with the wire from the tank sender the gauge removed connect a wire from that to earth and the gauge should go to empty showing a bad earth/connection/wire rather than float or sender.
Nigel Atkins

Yes-? sort of
If you get a full swing of the gauge by earthing it at the tank usually means the gauge and wiring to it are ok but the sender or it's connection are faulty
WARNING-------
Some gauges and voltage regulators don't like being fully earthed like this for very long so just a quick flick to get a result
William Revit

This thread was discussed between 13/07/2019 and 17/07/2019

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