fuel guage is wack

[bitchin85]

i topped my truck off yesterday and the needle went a little past full.. like always.. but it stayed there for 100 miles and then started going down like normal.. and then today i drove four hours, 200 mile round trip at about 60 mph at about 2200-2400 and it said i only used a half tank.. and i have a 20 gallon tank and i know thats not right.. so is it the guage? or the sending unit? orrrrr...... thanks guys

[tucsonjwt]

I had a similar issue a couple of months ago. You can get a lot of different suggestions on how to check for bad gauge or bad sending unit or bad ground. In my case, the gauge stuck at 1/4 tank, then read correctly when the gas in the tank was actually 1/4 full. I replaced both sending units (dual tanks) and that was not it. I replaced the fuel gauge and that fixed it.
I got the fuel gauge from Classic Parts for about $50. The ways I have read to check the sending units involve dropping the tank and fiddling with the sending unit connections/grounds - so for $50 I would just change the gauge first - takes about 30 minutes and you don't have to get dirty. If it is not the gauge, keep it for future use or sell it on Ebay to recoup some cost.
You will likely spend $50+ to have a pro diagnose it and he will likely be guessing also, It is possible to "bench check" both fuel gauges and sending units in a good auto electrical shop with proper test sets (checking variable resistance, etc.) but not worth my trouble for the $50 for a new gauge.

[bitchin85]

thinks ill check into that. the grounds should be good cuz when i swapped the tank, i re ran the wires off the tank.. probly the guage.. thanks