I purchased a Mel Pardue Auto Presido 5000 in mid to late 2008. I carried it a few times the first month, but not much after that. I ran across it today and tried it out. When I opened the knife it felt pretty weak, and after a couple attempts wouldn't even lock all the way open.

I was never overly impressed with the speed and force of the auto-action, but this was my first auto knife so I had nothing to compare it to.

Is it a spring or some other mechanical issue? Need to be lubed up or what?

sounds weak,send it back for a new one...........

Did you check the pivot tension? Is it lubed? Sure the kids didn't get in there and fire it like 10,000 times when you wern't around? Does not sound right.

pivot screw is probably tight.
possible lint/grit/grime contamination.
pobbibly wife/kids/pet monkey has fired it a lot.
random spring that went weak randomly.

best course of action, send it to BM
second course of action, purchase a t6 and a t10 and clean knife.
third course of action, replace spring with one from a place that sells KNIFE parts and knife KITS online. (also buy extras and possibly different sizes because shipping is expensive.)

Yet another idea that couldn't hurt: Take the 5000 and rinse the thing in a tub of hot water with dishsoap and let it sit for a few minutes before rinsing it off. Follow up with a blow dryer (hair, not paint eek on the low setting. Drop a little oil into the pivots and let it sit for a few before trying it again.

I do this a lot on 'sticky' knives and when I picked up an older 3550 it made a big difference in its performance.

This might not work on that knife, but it couldn't hurt either.

Sounds like the pivot screw is too tight, try backing off the screw a quarter turn and see if that does the trick.I have a few 5000's and a couple of them needed to be adjusted after sitting awhile.