Driver's side engine knocking noise

Knocking sound coming from valve cover driver side used my stethoscope to locate it. Crisp burning smell. Oil turns to black pretty quick. Thins out but no coolant and oil mixing! Freaking out! Changed the spark plugs did an oil change and did not help. Oil pressure has lowered from wheres it is usually at. Which is 3/4 of the way up now it is down to 1/2 or a little below one problem no dipstick. My engine size is a 4.2l 256ci.