2000 Saturn SL2

It sound's like she spun a rod bearing most likely it's possible to fix it by removing the oil pan. But you won't know until you remove oil pan and rod cap if the rod or crankshaft is damaged then your better off getting a used engine.

This is not going to be something your going to fix in your back yard. The motor will need to be rebuilt at the very least and even that could develop problems with crankshaft or block damage. A used engine may be your cheapest way out now but I would recommend a re manufactured engine instead.

While it's knocking take one wire off at a time then put it back on if the knocking stop's while taking any of the wire's off then those cylinder's have a problem in the lower end. The most common thing to happen on those engine's when running them low on oil is to spin a rod bearing.I have seen it happen a lot.