Fuel Guage Stuck on Full

[rickjowett]

Good Day,

Can anyone please give me some information on how to trouble shoot why my fuel gauge is stuck on full.

Thanks ...

[Forumadmin]

Hi Rick.
This is quite a common problem and usually requires removal of the sender and float from the tank. On an SA this is on top on an SC at the side.
To get at the sender on an SA you probably need to take out the boot (trunk) although it may be possible to drop the whole tank from its straps. This really depends on the amount of rust on the straps!
The boot is held by 2 nuts at the back and secured around the front with various fixings but over the years such fixings may have been modified. The rectangular box can then be slid out although you may have to remove the seat/steering wheel.
The sender may be stuck in position or the winding of resistance wire may have gone open circuit or the contact may be gunged up. You might find that driving with a half full tank of petrol over some hump back bridges might cure the problem.
It is also possible that the gauge itself is the problem. This can be checked by simulating the petrol tank sender with some resistances (or a spare sender).
Watch out at breaking the 3BA cheeshead screws when removing the sender.
viewtopic.php?f=2&t=2722&p=17575&hilit=sender#p17575
viewtopic.php?f=6&t=2009&p=10527&hilit=sender#p10527
viewtopic.php?f=1&t=642&p=3435&hilit=sender#p3435
The last showed a source of new units.

[rickjowett]

Thank you for your reply. I like your idea of riding over a bump to possibly jar it loose. I am trying to figure out if I have an SA or SC ??? Jupiter E2SAL813. Have a great day!

[Forumadmin]

20160426_190714.jpg

E2 SA therefore SA. SC has a trunk with a hinged door rather than just a compartment behind the seat.

20160426_190722.jpg

The resistance of the coil is about 70 ohms although I have not a working one in my spares to properly test.

You can see the two thin copper fingers that slide along the coil on the left. They move to the right as the tank goes empty. Note that showing full indicates a short when empty the resistance is 70 ohms.

[rickjowett]

Thank you very much for all your help
I wonder if I can snake a coat hanger through the filler hole and bump the float arm loose? Something I may try. Looks like a tough job to remove the sending unit.

[Tony Fearn]

Hello Rick.
Here's a site I found which describes the workings of I suspect a more modern car sender unit, but the basics are probably the same.
http://auto.howstuffworks.com/fuel-gauge1.htm
Tony.

[Srenner]

Here's one of my secret info sources: MGAGuru.com . Many of the Lucas Items on the Jupiter are the same or very near the same. This site is a great example of getting a knowledge base out to the people who own the cars (and use the internet).

Germane to the topic: http://mgaguru.com/mgtech/electric/fg115.htm and http://mgaguru.com/mgtech/electric/circ_f1b.htmThere are multiple pages on the sending unit, including dissection of Moss replacements, how to rebuild yours, etc.

Range on the unit should be 0 to 70 ohms. The most common failure from use is that the very thin wire breaks at the pivot arm which is where it grounds. No ground means full tank all the time!
Cheers,
Scott

[rickjowett]

Hi Tony,

That was a really helpful artucle, thank you.

Rick

[rickjowett]

Hi Scott,

Thank you for the excellent links, this is very useful information. Any chance that the float is stuck in the up position, or do you feel like its a wire break?

Rick

[Forumadmin]

If it is stuck up the resistance is (or at least should be) zero if the wire is broken the resistance is a lot.

[Edmund Nankivell]

Does anyone know, are new tank senders available and if so from who, where?

[rickjowett]

Great News. I fixed the problem. I ran the car till about half full, then went over a speed bump a few times hard and voila, it worked. Apparently filling the tank full caused the internal lever assembly to hang in the full position. The speed bumps jolted the lever arm free and since there was only a half tank of gas the float/lever was not supported by fuel and was able to fall down, it just needed help. Moral of the experience, always search out the cheap and easy fixes before taking things apart. Thank you all for your ideas.

[Tony Fearn]

Wonderful. Just the same as George (Pre-war section) would have tried first.
Tony.