I have just replaced both hood lifters on my 92 Z28.The ones I had on there were completely shot and I had to hold the hood up with a piece of wood!The new ones although they take soft of the lift on the hood when i open it they dont keep it up and it falls down again.Are these the only supports that hold the hood up or is there a prop too?

 

The hood struts are all that hold the hood up, no prop rod.

 

The hood seems to be too heavy for the struts.I bought these New old stock maybe they are no good

 

If they're NOS, then it's possible that over time they lose their charge, as did your original struts.

 

It sounds like there is something wrong with the lifts... When you open your hood it should not come up right away, but at around 12" or so take off and lift all the way on its own... thats how mine work when they were new... THey shouldn't sag once in the up position...

Personally I would take them back...

Some places have a LIFETIME warrenty on them, I took mine back after 5 years and they honored it, they were all disgruntled, and told me I installed them wrong and thats why they failed, but they were under warrenty and had no other quams. Murrays has the lifetime