TR2/3/3A Fuel sender or gauge?

[Hermund]

Hi there.
Problem: My fuel gauge never shows more 1/4 full, even when "filled up".
But when the tank is really less then 1/4, the gauge starts working and shows almost accurate on it way to empty.

Now I've tested the gauge (Jaeger FG2530/20) by disconnecting connector T, and it passed the test described i "service manual".
Today I looked at the sender(FT3331/02), measuring ohm. the tank is well over 1/2, and I have a reading of 57 ohm. When pushing the float a little down, the reading changes accordingly, 45-50 ohms. My conclusion is that it works. Also disconnected the connector to the gauge(on the sender), and the gauge shows "full".
Connection ok, as far as I understand.

I've put on a new earth cable on the gauge, and checked the earth on the sender also. Seems ok.

I was quite sure the fault was at the sender end, so the instrument panel is all assembled, and I hate to take it out again and find nothing..

Question: I started to think (that is always dangerous), but is it possible that the two connectors on the gauge are swapped? will that create something like this?

Looking forward to suggestions

Pardon my English, but a Norwegian living in France..
I say no more

 

[Geo Hahn]

Been a long time since I fixed mine so I do not remember what results various failure modes and mis-wiring would produce.

This is the site I used then - it is for an MGA but I think the gauge works the same way on our TR3s:

https://mgaguru.com/mgtech/electric/fg_01.htm

 

[CJD]

Have you made sure the float arm is not snagging the side of the tank? It sounds like maybe the float is not rising fully when full.

 

[Gliderman8]

I had a similar problem with my TR6. It turned out to be the plastic float was filled with fuel. A new brass replacement and it is working.

 

[M_Pied_Lourd]

Have you made sure the float arm is not snagging the side of the tank? It sounds like maybe the float is not rising fully when full.

+1

 

[dklawson]

Give a read through the fuel gauge pages on the MGA site that Geo posted the link to above.

Good clean ground connections are required for the magnetic gauges to work properly. I know you have run the new grounds but make sure all the connections are clean and that the new ground wires are making good contact with the gauge and sender.

A leaky float as Elliot said is also quite possible. There is a Ford brass float (# COAZ=9202-B) that can be used in place of the Smiths one. You will find them on eBay and many online suppliers.

While it could be a bent float arm snagging on something in the tank, that is less likely if the gauge ever worked properly for you.

 

[Hermund]

Thanks for a quick response, guys!

I have never seen it work properly, neither has the previous owner.

The floatarm is floating freely, on the surface. When I push it down, the readout of my instrument changes as expected.

Earth is usually a problem, and for my sender unit, the connection to Earth(under the tank) doesn't look too good, somewhat rusty. But, on the other hand, measuring between sender earthconnector and earth on the dash, I get a clear, no hesitation, "beep" from the istrument, and it shows zero ohms. I will find more good-looking solution to that.

I've been on the MGA site before, but used the "shortcut". I'll do it the hard way now.

By the way, no one commented on my question. Will swapping turn the needle around?

 

[dklawson]

By the way, no one commented on my question. Will swapping turn the needle around?

The "T" terminal on the gauge must receive the green/black wire from the (fuel Tank) sending unit and the "B" terminal must receive power from a switched source (... from the Battery). The gauge will not work right if those connections are reversed.

 

[6TTR3A]

Hermund,
Take your test one step further: You said when you pushed down on the float, the resistance decreased
(which is correct) Now make a hook of some sort and pull the float UP as far as you can. The resistance
should now increase to as much as 85-90 ohms. If it does, it's the sender. As others mentioned, either
the float is leaking or dragging on something. It is possible to incorrectly install the sender. If the screw
holes on the sender are offset either one to the right or one to the left, the float will drag (and stop) on
the side of the tank. I would suggest removing the sender completely, reconnecting the T wire and the
ground wire, then moving the float thru its arc by hand. If the gauge registers properly, you've isolated
the problem. If the float appears to be empty, it was dragging. If it has petrol in it, find the hole,
enlarge it, drain it and solder the hole closed.