my 1993 chevy caprice was losing oil pressure now im hearing some knocking what could it be

Have you checked your oil level? How long since last oil change? Either could cause low oil pressure. Your knock could be several things. With low oil pressure I would suspect your hyd lifters not getting proper amount of oil to work properly. Is knock high in the motor (around valve covers)or does it sound like its down in the oil pan area. (Way under your car)?

yes i change the oil and went to a thicker weight it sounds like its down in the lower part of the car

Connecting rod thrown or journal cap

I agree with DavidH25.

what is a journal cap and where is it located

http://en.wikipedia.org/wiki/Connecting_rod

With no oil pressure it does not take long to burn it up, a tremendous amount of friction from the piston pushing

I didn't mean to just 'take over' dandy...just my 2 cents

scorched cap from no oil

Oh it's ok. You the man for this job. Your 2 cents will get them a lot farther down the road than mine. Lol

bout how much will this part cost and the labor work

In my opinion if your going to go as far as repairing that you would be better off in the long run to do a complete rebuild. If lack of lubrication caused the issue there are several other areas that will also be in need of repair.

Agreed. We don't know as fact that is even what is knocking, it's our best idea though. The cap, if you can even buy just one, is dirt cheap but the crankshaft is also going to have the same issue, the rod will have to come off the piston, you have to get to the wrist pin, meaning heads have to come off (the piston won't come out from the bottom except on some race cars that are set up to swap pistons in a hurry from the bottom)...major surgery no matter how you look at it. Think about a long block crate engine. I know, easy for me to say, I couldn't afford it. Rebuilt $1100, used from eBay $400