Fuel gauge going crazy!!??

[TruAggression]

On my 87 305 tbi my fuel gauge like first thing in morning or after not driving for a little while will go up to being full then stop and shoot back down to about 1/4 of a tank. If the truck's hot it will just stay down to between empty and 1/4 tank but there is way more gas than that in it. I've checked the ground at the neck its good sanded down to bare metal and put it back on still the same. You think its the actual sending unit in the tank or fuel pump just trying to get a good guess before I throw parts at it. or gauge itself bad its been fine for about a year now and 15,000 miles of driving this is the first thing kinda messing up on it and input would be greatly appreciated.

Josh

[Slonaker]

This may or may not be helpful...but when my temp gauge was going crazy like that, it was a crack in the insulation letting the wire to the sender ground out intermittently on the valve cover. Your wire could be doing the same thing somewhere on the body or frame.

Also, a hot rod builder friend of mine pointed out to me that our gauges swing back and forth a lot because the tank is long and skinny. It is affected a lot by acceleration, deceleration, and inclines.

Slonaker

[TruAggression]

I dont see any wires or anything screwed up yet that I can see yet. Yeah i know the gauge does that but its not from that like right now tonight i topped the tank off and my fuel gauge shows 1/4 tank but in the morning tomorrow ill start it up and the gauge will climb to where it should be at ful the shoot back down to 1/4 tank. Weird right?