TR2/3/3A TR3A fuel gauge

[tmc]

My newly installed fuel gauge in my TR3A (TS45911L) flickers when I turn on the key, but doesn't register correctly. Somewhere in the recesses of my mind I remember reading something about calibrating a fuel gauge. In this case, everything is new or rebuilt.......the gauge, the wiring, the tank sender. Can anyone shed light on this? How does one do such a thing?

 

[NutmegCT]

Here's the system I used when I calibrated my own gauge:

https://mgaguru.com/mgtech/electric/fg_06.htm

I also had to put a new pointer on the gauge. That was more challenging than the calibration!

One thing to check first: be sure the gauge is wired in correctly, and that the wires themselves aren't burned through and/or have corroded ends.

Tom

 

[TR3driver]

be sure the gauge is wired in correctly,

Which includes making sure it is securely grounded. Mine became a whole lot more repeatable when I added ground wires for the gauge and tank sender.

 

[tmc]

Here's the system I used when I calibrated my own gauge:

https://mgaguru.com/mgtech/electric/fg_06.htm

I also had to put a new pointer on the gauge. That was more challenging than the calibration!

One thing to check first: be sure the gauge is wired in correctly, and that the wires themselves aren't burned through and/or have corroded ends.

Tom

Thanks for the connection with the article. I don't have the resistors, but I know how many gallons are in the tank and what it's capacity is, so if I can adjust my gauge to be semi-accurate, that'll be fine. I do have a ground wire on the sending unit, but not on the gauge. I'll look into that, too.

 

[Don Elliott]

I have the original sender and gauge in my 1958 TR3A. When I fill up the tank, my gauge reads full until I have driven about 60 to 100 miles. Then it suddenly jumps to about 3/4 full. From that point down to almost empty, it behaves as it should.

It's been this way for over 22 years.

It's not a problem, but does anyone have any suggestions?

 

[TR3driver]

Good place to start would be to learn if the problem is the gauge or the sender. Fill the tank and measure the sender resistance with the gauge disconnected from it. Drive 20 miles or so, check again. Repeat.

My TR3 still has its original gauge & sender AFAIK; and it isn't very linear either. Like yours, it reads full for several days (40-60 miles) after a fill-up. But then it starts falling slowly, but more or less evenly. Below 1/2 tank indicated, it starts falling more rapidly; so its less than 40 miles from 1/4 to empty. It probably just needs better calibration; but could also be that the variable resistor in the sender is worn out. They do wear over time, and generally the wear is the worst in the middle of the range.

BTW, the article linked to above is for a MGA, which doesn't have quite the same resistance range as the TR3-4. If you want a really good calibration, you need to measure your sender and calibrate the gauge to match.

Resistors with leads are getting harder to find, but are still fairly cheap when you do find them. Eg,
https://www.radioshack.com/product/index.jsp?productId=2062304
(I found a better assortment at my local electronics shop, but those are getting harder to find, too.)

PS, Hopefully this is too obvious for words, but JIC : You can always combine multiple resistors to get the value you want. For two resistors in series, the total resistance is the sum of each resistance. Eg, to get 1200 ohms you could combine a 1000 ohm and 200 ohm resistor in series (ignoring the effects of tolerance for the moment).

For resistors in parallel, the formula is more complicated. 1/Rtotal = 1/R1 + 1/R2 Thus for the example of a 1000 ohm plus a parallel 200 ohm, the result is 1 / (1/1000 + 1/200) = 166 ohms.