Same for me. Mine had no weight or OEM wing stock.
New lifts is the answer. The ones w/OEM wings I believe had different lift shock on them and they also had a weight. Never checked the details for sure. Maybe those OEM ones would work for us.

 

I just put in my nismo rear spoiler and having problems keeping the hatch up. what is everyone else doing to counter this problem?

 

I had my struts rebuilt by Frank at Strutwise in Canada. My hatch stays up. period.

 

who is frank and how can i get it done to my car?

 

www.strutwise.com

Call 602-589-1200 ask for Frank. Make sure he understands you have a 350Z because the 300ZXes up there have the problem too.

 

I started having problems with the stock hatch lifts a few months after having my NISMO Rear Wing mounted. Long story short; my dealer told me the NISMO Wing is supposed to come with stronger lift shocks to support the extra weight. My car was already in the shop for some minor body work when the wing arrived. I had it delivered straight to the shop for installation without checking the contents first (I know, my bad), so I can't say for sure whether or not the replacement shocks were actually included. Nonetheless, I asked my dealer to order a set of these "stronger" replacement shocks. They came in, where installed and I haven't had any problems with the lift falling. I can feel the difference in the resistance when closing the hatch. These shocks are a bit pricey, IMO but they solved my problem and the dealer "felt my pain" and gave me a 50% discount. No more headaches (literrally)

Rod-Z-Guam

 

The new hatch shocks held the hatch open, but the problem was that the lock would not disengage without me pulling up on the hatch as I opened the lock. After installing the new shocks, everything was fine for about a month, and then the lock issue reappeared. Removing the weight has fixed that for one year now.