Propshaft Posted June 1, 2023 Report Share Posted June 1, 2023 After 4 years of ownership my fuel gauge now has decided to always show full when switched on .I have checked the connections at the sender unit cleaned them I checked I there is power 11-6 volts . What next take out the dash and check the power cable for resistance ? What is good resistance? What next? Any suggestions would be appreciated hope I can bottom it before I take on the RBRR Quote Link to post Share on other sites
HowardB Posted June 1, 2023 Report Share Posted June 1, 2023 Sheet 3 of my attached drawings gives the detailed circuit and resistances of the various components. Hope this helps & look forward to seeing your car at Knebworth with a fully working fuel gauge. Howard PS I drove my new replacement Tr7 V8 with totally unknown fuel consumption on the RBRR without a fuel gauge and during the fuel strike a couple of years back. 1981 TR7 DHC Wiring Diagram Rev 7 03_2023.pdf Quote Link to post Share on other sites
RobH Posted June 1, 2023 Report Share Posted June 1, 2023 (edited) For the gauge to show full all the time, either the sender may be stuck at the low resistance end of its travel or there may be a short to earth somewhere in the wire from the gauge to the sender. An open circuit would show empty all the time. First check would be take the wire off the sender and the gauge should go to empty. If it does, the fault is in the sender. If it doesn't the fault is in the wire or perhaps the gauge itself . Edited June 1, 2023 by RobH Quote Link to post Share on other sites
HowardB Posted June 1, 2023 Report Share Posted June 1, 2023 When the tank is full the resistance is 10 Ohms and when empty 300 Ohms so disconnecting the sensor Quote Link to post Share on other sites
Propshaft Posted June 2, 2023 Author Report Share Posted June 2, 2023 Ok took the wire off the sender unit and the gauge went to empty does this look like a new sender unit if I remember rightly the last time I filled it i really brimmed it could this have caused it? Quote Link to post Share on other sites
Propshaft Posted June 2, 2023 Author Report Share Posted June 2, 2023 Just an add on to my last post the sensor looks quit new the anodising is still on also when I remove the sensor should the gauge show when I move the float Quote Link to post Share on other sites
RobH Posted June 2, 2023 Report Share Posted June 2, 2023 If you earth the sender body, the gauge should follow the arm position. It will be a slow-ish change, not immediate, because the gauge is a bi-metallic thermal one and the temperature has to rise or fall for the needle to move. I suppose it is possible the arm got stuck somehow if the tank was really full. Quote Link to post Share on other sites
keith w Posted June 3, 2023 Report Share Posted June 3, 2023 I had to chase my fuel gauge system through last October. I had a new sender ready and waiting but wasn't convinced the one fitted was duff. I established the gauge was faulty and replaced it with a known good one from Steve Wilcox, then I jury rigged the new sender on the end of the wiring under the car but not fitted inside the tank. That all checked out fine so it just remained to put some fuel in it to see if the existing sender was good. I'm pleased to say I pit two gallons in today and the gauge went up to 1/4. Problem now is to get it running again. Quote Link to post Share on other sites
Propshaft Posted June 3, 2023 Author Report Share Posted June 3, 2023 Thanks for everyone’s help I will be looking at all this next week and pass on the results Quote Link to post Share on other sites
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