Bench testing two cheap eBay fuel sending units

That is interesting information, thank you.

What intrigued me was that neither of the sending units I tested behaved the same tested on the bench as they did on the car. On the car they drop off from Full much too quickly and in fact read 1/4 tank with approximately 12 gallons in the tank. On the bench, they REACT smoothly to downward changes in the arm.

Not only that, but these gauges react so SLOWLY to changes in the float position that I'm not convinced that the discrepancies at different points in the chart matter. That float is moving all the time and that combined with whatever buffer feature the gauge or reg has makes it even less of an issue.

What also leads me to conclude that the issue lies in the car's wiring or gauge is that several people state that the sender measures out fine, but they can only get 5/8 on the gauge. Those gauges read lower the more resistance there is in the circuit, so that tells me the issue is internal to the car. I bet if you took a known good gauge and ran it through an IVR but right at the tank, the mysterious 5/8 reading would miraculously turn into FULL lol.