My hood will not stay open either, ever since I had it repainted and the car restored. Either the problem is:
1. The spring has lost its "spring" (which I find hard to believe)
2. There is a problem with the plastic catch (mine is new)
3. They did not put enough torsion (revolutions) in the spring before they inserted it into the hood.
4. Who knows???
I have taken it to 3 dealers, and several other shops, and no one wants to even try and repair it, since they are all afraid of damaging either the paint or hood in the process.
Any ideas?