I have had three, new fuel-level senders and all have had problems.
First one, in left tank, only showed a reading, of half full, when tank was half full. More or less fuel showed empty on gauge. Second, new sender seemed to be accurate until half full, then stayed there as tank went lower. Same problem on right tank with a new sender.
Problem is not the gauge, as it has been verified by a Jaguar shop using a calibrated, bariable resistance.
Senders should of course be tested out before mounting, Stuart - connected to the gauge or an ohm-meter. The gauge reacts slowly, but in either case will show resistor continuity - which ‘may’ be rectifiable if faulty…
Another problem is that the units are ‘sided’ for either ‘left’ or 'right, and the float rods are easily bent - causing hang-ups against the tank sides. Hence verifying the electrics will save time - and if failing after mounting - confirming hang-up as a cause…
The set-up is not famous for its precision, partly due to the tanks shape - but can be trimmed by judicious bending of the float rods…
Remove the senders and move them by hand to see what the fuel gauge does.
The floats might be full of fuel.
The arm could be jamming inside the tank.
The senders, even the OEM, could need calibration (doable).
This is very true. I managed to get mine to read well by bending the arms a little. I have one of the printed variety and one old school resistive coil type. It’s a bit of a nuisance in a series one as the sender goes in at the bottom of the wheel arch.
Years ago, the floats on my 1987 series 3 XJ6 suffered from the first two symptoms you described. Floats sprang a leak and filled with fuel, and the arm jammed against the side of the tank. I’ve given up on the validity of any readings I get on my fuel gauge. I just keep track of how many miles I’ve driven since my previous fuel purchase, assume a worst case scenario of my average miles per gallon statistics, and fill up accordingly. The good news is, in nearly every case, my fuel consumption figure is much better than I’d expected, even topping 21 miles per gallon on a long highway trip.
Same here, I had 2 new ones fitted and the results have been consistent. By that I mean consistently inconsistent. So its a case of refilling after 250km max in each tank. Thank goodness the odometer is accurate.
My mileage (in US MPG) is only around 13 for general running, 16-17 on a run. Which considering mines a manual which is supposed top be more efficient is not good.