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MG MGA - Fuel gauge jumps around

I got tired of my old fuel gauge not reading correctly (it only went from empty to half) so today I installed a new fuel sending unit in my fuel tank; and now the needle jumps around when I go around corners or over rough road. I don't remember the needle jumping around like this before even though it didn't work correctly. I got the new unit from SF and it only had one pick up arm instead of the two arms on the original Smiths unit. Before I installed the sending unit I removed the fuel gauge from the car and adjusted it per Barney's instructions so on the workbench it read correctly at empty, half and full.

In the car the fuel gauge also reads correctly when the car is stationary or on a smooth section of road. Is there anything I can do to stop the wildly swinging needle?

Thanks

Andy 60 Coupe
Andy Preston

I have an original sending unit that was rebuilt by Nisongers. The tank is new. My fuel gauge does the same thing when driving. I have to wait until I'm on a straight level section of road to get a reading. Reads accurately when still. My guess is the baffles in the tank (or lack of them) causes the fluctuations.

Cheers.

Larry
York, Maine
Lmazoway

That's how they are, as original. The gauge just reads voltage varied by the sending unit resistor. You get good at mentally calculating mean values! Later type gauges work on a heating element so they are damped, taking all the fun out of it.

FRM
FR Millmore

The MGA fuel gauge is generally accurate, in real time. What you are seeing is accurate indication of the fuel sloshing around in the tank with instant variation of the reading. It's the nature of the beast.
Barney Gaylord

Thanks guys, I was hoping there was some kind of voltage stablilizer that I could add to the circuit to dampen the movement; apparently not. I'll just have to get used to the needle moving all around a lot. At least I now know when I'm getting low on fuel.

Thanks

Andy
Andy Preston

Andy, I always look at these gauges as an indication that there is fuel in the tank. If the gauge is jumpingg around there is fuel there. Set the trip meter and establish how far you can travel before filling up , leave a 50 mile margin to be safe. Between these two indicators you should not have to walk home too often. Sean
S Sherry

This gauge may be very accurate when near empty if you know how to use it. Rock the car a little, and if the needle wavers you still have some fuel. The amount of needle wavering when near empty can be a good indication of the amount of fuel left, especially when it's down to less than half a gallon. When it stops wiggling you better know where the next gas station is, figuring it's under a quart and maybe 5 miles to go (if you were paying attention).

If it runs dry and starts to sputter, you can maybe nurse it along for another mile or three, if you understand how to run in super economy mode and nurse the last dribble out of the tank. Been there on many occasions, and almost never have to walk.
Barney Gaylord

Hey Barney

Why not share your method of "super economy mode" with the rest of us?
F Valenzano

I also suffered of similar issue, and my thought was to maybe add a small capacitor in parallel with the fuel gauge input side (next to the gauge), to electrically dampen the signal and reduce needle moement.

Of course I have no idea at this stage of what the right size capacitor would be as I have not tinkered with it yet.
Maybe someone has done this before?

Gonzalo
Gonzalo Ramos

F V, -- I will post "super economy mode" in a separate thread.

Gonzalo, -- This is a low voltage and very low frequency signal, also maybe higher current than you might think, so would need a VERY LARGE capacitor to make that work. The sloshing frequency may be about 1-Hz (one cycle per second).

What is needed is an electronic sampling and averaging circuit that would sample the signal maybe 5 times per second for two seconds, then do math averaging, and set up a new average signal (resistance) to the gauge "T" terminal after each sample. If you make a hard turn left then hard turn right that might last two seconds each way, you may still see the gauge needle waver slowly.

If this is too much of a challenge, or you want it to be slower yet, then change the fuel gauge (and matching sender unit) to a later model thermal activation unit, in which case it will work like a later model MGB, nice and slow acting. This also wants a voltage stabilizer to eliminate normal sudden fluctuations of system voltage.
Barney Gaylord

This thread was discussed between 02/11/2010 and 07/11/2010

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