I'm changing fuel tank because old unit developed quite the leak, and seeing how it's impossible to buy a new tank for the old beast I had to get used one. New(used) tank came with a sending unit already installed, so I just left it in place, swap the pump and the last thing I did was to check fuel quanity circuit to make sure it works well, it does, well almost. WHen float is all the way up the gauge reads 3/4 full.
Now I took the quanity gauge apart looking for some sort of calibration screw, there is one there but it look pretty delicate and I'd like to know for sure that in fact that's the only way of calibrating the gauge. Any suggestions ???

Bending the float rod is the only way I know of. By changing anything, you trade driving for a long ways before the gauge moves. For driving a long ways at or on empty. On my Troopers when the empty light comes on, you have about 2.5 gallons of burnable gas, if you don't turn the truck off <img src="/forums/images/graemlins/lol.gif" alt="" /> . One gallon useable if you turn the truck off. Don't ask how I know <img src="/forums/images/graemlins/smile.gif" alt="" />

I believe that strip w/contacts at the end is a protection device (bi-metal) for the guages when a surge may occur at startup. The screw is factory preset for adequite tension to close the circuit. My '88 Trooper has it on the temp guage but in '89 it was moved to the fuel guage. My Troop had dead fuel and temp guages until I removed the cluster and cleaned those contacts.
I too had eratic fuel readings (which was better than NO readings) and pulled, cleaned and adjusted my sender with minimal favorable results. Seems Isuzu has been plagued with fuel sender issues, but each one has its own peculiararities and can be understood by the driver in time. If every vehicle had to have a qwerk I think I'd rather have it in the fuel guage than, say, front suspension or transfer case!

Waaaayyy back in about 91 I had some knucklehead put a trailer connection on my trooper, it shorted out the gas gauge so it read full all the time. It was many years before I got it fixed, and now it reads from no more than 3/4 full when full to well below zero, and erratically... I use the odometer.

Now YOU may well benifit from turning that tiny screw in about 1/2 turn or cleaning those contacts (or both). Could also be the windings in the sender, but wiring lights into a normally grounding reostatically controlled system had to produce excessive heat (current). The sender's coil is hefty, the guage winding is micron thin. Worth a try and easy to do.