the problem with my car is the fuel gauge works when it wants to its a 1979 corvette would it possibly not be grounding good because i've checked everything else out and cant find anything

I believe the '79 fuel gauge is in the tank like C4s (my '91 for example) if so they are notorious for having the contacts go bad. I don't know for sure about the '79 but I don't think it 's that bad of a job to pull it and check/clean it. Also possible it's the gauge too but much more likely it's the sender in the tank.

1968 through 1982 Corvettes are notorious for poor gauge performance and the fuel gauge is second only to the clock for failing without warning. Your's is warning you, its either the gauge or the sending unit, there is nothing between the two but 16-gauge electrical wire and fiberglass.