Any mechanics out there?

[bars full auto]

The gas guage on my CJ-7 works but doesn't work right. I can fill the tank up and it only shows 3/4 of a tank. I grounded the wire coming out of the tank and the guage reads full. This should mean that my sender is good. What could be wrong with my guage? Thanks for the help.

[WARWOLFx]

Float is messed up. Hope that wasn't to technical for ya :D

[ED4x]

Actually it sounds like your guage is ok and your sending unit is messed up.

The guage is just a ohm meter that measures resistance. Since it goes from full to empty with out stopping there should be nothing wrong with it.

The sending unit has a variable resister on it and the resistance changes as the float level changes. The first thing to check would be the float and the float arm(on newer vehicles with electric pumps they don't use float arms just a captured float around the variable resister) and make sure the arm isn't bent or binding and your float is intact and not deteriorating. It they are good hook it up to your guage turn the key on and move the float and see if it goes from full to empty with out stopping. Sometimes there will be a bad spot on the variable resister.

Hope this helps.

[Mac_Muz]

This might be a good thing....my wifes car does the same thing, and I never bothered to fix it as she has a 4 gallon reserve. LOL
But it might be the wrap on the sender is bushed out and the reading is off for it. Or it might be the adjustment tabs are out of adjustment. The fact that the gauge works properly when you ground the wire says the wiring from that point on is good as is the gauge.
The problem is inside the tank. So get the fuel level down some, then get the sender inside the tank out. If the wires there are bushed and fuzzy from the contact slider cutting them replace the unit. You will still have to set the unit.
You will find a top and bottom stop for the slider/ contact.

With the sender in your hands and a friend set it to above dead empty to read empty. (So you have a bit of reserve) Then set it to the full setting, but be sure the float will not top out on the tank to read full.

Ever notice some cars seem to read full for a long time before dropping? That is due to a float that says full, but is set too low.

Hope this helps....Mac