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Thread: gas gauge or sender or ???

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    gas gauge or sender or ???

    57 tr3. been restoring it for a few years, got it running just a few months ago. been working through problems as the stupid mechanic who supposedly put most of this together before abandoning this project "because i wasn't happy". gas gauge was supposedly rebuilt etc a number of years ago. sending unit is relatively new; maybe 6 months? replaced the sending unit because the old one, also supposedly new a number of years ago, did not register anything at all to the gauge (as far as i can tell, never worked). how do i test the sending unit?

    gas gauge reads dead empty until something over 1/2. then it jumps to 1/2. as soon as you start driving, it varies (with 1/2+ in the tank) between 1/2 and full, and skitters a bit. all other gauges seem to work properly.

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    Re: gas gauge or sender or ???

    just found this: The TR3 units should read about 110 ohms EMPTY and near 5 ohms FULL

    is that right?

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    Re: gas gauge or sender or ???

    No, that is backwards. The TR3 gauge works differently than the later cars; reads less full for lower resistance. Sorry I don't recall the range offhand, but I know open circuit is past full.

    But you're on the right track. Check the sender resistance as you move the arm; it should change smoothly and more or less evenly from empty to full. You can use a yardstick through the filler to push the float down, or a bent coat hanger to pull it up.

    Once you find out what the correct range is (or just accept what you have), you can use the techniques outlined at https://mgaguru.com/mgtech/electric/fg_06.htm to test the gauge. As Barney shows on that site, there are two nuts on the back that allow for adjustment, but they are tough to get right. I found that just being mounted in the metal panel made a difference in the reading as well.

    Another tip is to add a ground wire for the gauge. The factory ground through the mounting clamp is far from secure. Just a simple jumper from the mounting stud to the nearby ground tie point on the instrument panel will do. I also added a ground wire for the tank sender, since otherwise the tank only grounds through the fuel line.

    You can see my fuel gauge ground wire in this photo (taken as I was parting out my previous TR3A after it got wrecked).
    Last edited by TR3driver; 04-01-2016 at 01:39 PM.
    Randall
    56 TR3 TS13571L once and future daily driver
    71 Stag LE1473L waiting engine rebuild
    71-72-73 Stag LE2013LBW waiting OD gearbox rebuild

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    Re: gas gauge or sender or ???

    Hopefully an adjustment is what you need but when my gauge was erratic and only stopped at some points on the scale I used the website Randall linked to and found one very thin wire broken inside the unit. I carefully repaired that break and all has been well since. I do not recall which wire it was but I do recall it seemed about as fine a human hair.

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    Re: gas gauge or sender or ???

    given the erratic nature of the gauge, i'm going to try grounding it first. hopefully that will solve the problem. if that doesn't work, mgaguru is quite a resource! thank you for all the info above.

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