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 Post subject: Fuel gauge sender
PostPosted: Sat Apr 13, 2019 7:30 pm 
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Joined: Wed Dec 18, 2013 5:05 pm
Posts: 293
I have been unable to get my long door car fuel gauge working.
Initially it didn't move off empty and the electrician identified the sender as the problem. I am aware that the earth is usually the problem with these things and have put an earth wire in from the sender cover to the tank mounting bolt. The electrician said this earth is OK.
I pulled the sender out and dismantled it to find the insulation between the power stud and the top cover was breaking up. I replaced the insulation. With the sender out of the tank I attached the power lead and earthed the cover, with my earthing wire to the mounting bolt, and the sender an gauge worked perfectly.
I refitted the sender to the tank and the gauge reads full all the time. I have tried earthing it through another wire to no avail.
Any ideas please.


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 Post subject: Re: Fuel gauge sender
PostPosted: Sun Apr 14, 2019 7:18 pm 
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Joined: Wed Dec 18, 2013 5:05 pm
Posts: 293
This morning I removed the sender again and pulled it apart. I cleaned up all the surfaces and removed the bit of insulation I put on the stud under the cover. I noticed that the gauge stayed on full until the float moved up a bit at which point the gauge went to empty. It then rose normally as you lifted the float.
The tank had 15 litres in it so I thought the float should be high enough to get the gauge to work. I put another 10 litres in and now the gauge reads, but only about 1/8 of a tank, with 20-25 litres in it.
It will now read full when it is full but it will read empty with about 15-20 litres still in the tank. Reading empty with 5 litres left would be good.
I tried to bend the arm down but I didn't want to strain it for fear of it snapping, it is 64 years old.
However, the gauge does show a fuel level which is better than yesterday. In the absence of any breakthrough ideas I will leave it and see what happens as the car gets used.


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 Post subject: Re: Fuel gauge sender
PostPosted: Tue Apr 16, 2019 11:44 am 
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Joined: Thu Dec 19, 2013 9:35 am
Posts: 76
Earthing the casing is only part of the solution as the sender works on variable resistance between the coil and earth through the float arm.
The correct resistance should be 75 Ohms for Full and 0 Ohms for empty. I believe this is linear so you may be able to locate the point of error.
The best I could get was 75 and 1.3 after fitting an earth wire between the casing and the centre pivot of the float arm.

Check that the terminal on the float arm is touching the coil correctly through the full stroke as worn bearings will possible cause problems.


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 Post subject: Re: Fuel gauge sender
PostPosted: Tue Apr 16, 2019 7:24 pm 
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Joined: Wed Dec 18, 2013 5:05 pm
Posts: 293
fingoon rob wrote:
Earthing the casing is only part of the solution as the sender works on variable resistance between the coil and earth through the float arm.
The correct resistance should be 75 Ohms for Full and 0 Ohms for empty. I believe this is linear so you may be able to locate the point of error.
The best I could get was 75 and 1.3 after fitting an earth wire between the casing and the centre pivot of the float arm.

Check that the terminal on the float arm is touching the coil correctly through the full stroke as worn bearings will possible cause problems.

Thanks Rob. I got it working. It turned out that the small lugs that limit the arm movement were allowing the arm to descend a bit too far allowing the arm to move off the rheostat windings. I put a few extra litres in the tank to raise the float a bit and all is good.
It is about as accurate as most of them but it works and is perfectly usable.


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