Okay so I have a 2004 Jeep Liberty. Last night, the car cut off while I was in reverse backing out of the driveway. When I tried to crank it up after that, it would crank most of the way up and even stay on for a couple seconds but then cut right back off. We tried jumping it off to see if it was the battery but that did nothing. Then this morning when I tried to crank it up, it was making a very loud knocking noise. Not sure if it’s related to the problem- but when we checked the oil it was extremely low. I just put 2 quarts of oil in it less than a month ago and it had just had an oil change not long before that. I am having it looked at today but would really appreciate some feedback. Thanks guys!
Oh and I also just recently got new spark plugs.
How many quarts low is the oil right now? Regardless, from the information you’ve put here so far, it seems likely that you’ve run this engine while it’s seriously low on oil and permanently damaged it. If that’s the case, that’s a shame, as that could have been avoided if the oil level were kept up.
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Did the engine actually start this morning when it was making the loud knocking noise, or did it just turn over but not start.
Either way, a knocking noise is usually a very bad sign.
As far as the low oil goes, you may have a leak or the engine is burning the oil that fast.
This is a good example as to why you should check the oil level once a week.That may have saved you from an expensive repair.
In my own history, my wife has somehow gotten a little pin hole in two oil filters…most likely from road debris, likely from a stone thrown up from the road.
Had I not noticed the fresh oil stain where she parked, it would have been a costly repair.
Yosemite
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Sounds like you ran the engine low on oil and destroyed it internally. Knocking $ounds are u$ually very expen$sive. Get ready for a very large repair bill. Sorry.
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I’m inclined to agree.
Rev the engine by hand while listening under the hood. If the knocking turns into a rapping sound, you’ve toasted the bearings. The rod bearings are the first to go. The crank bearings have more surface area, share the shocks of the combustion with their neighboring bearings, and are second-order impact. The rod bearings have less surface area, cannot share their shocks with the other rod bearings, and are first-order impact. The lateral shocks hit them first and they’re each on their own in dealing with them.
I’m fairly certain that on this vehicle the engine needs to be pulled to replace rod bearings. That gets expensive. Besides, if the oil ran so low that the pump started pumping dry air, there’s likely other internal damage.
The good news is that on your replacement vehicle you’ll (hopefully) have learned the cost of neglecting your fluids. Especially the oil.
Sincere best. And I mean that.
Based on your report OP, I think you may looking at an expensive fix. But no way to know for sure via the internet, you’ll need someone skilled w/the Jeep in front of them to know for sure. On an optimistic note, there are many things that can cause knocking sounds which aren’t expensive to fix. Exhaust leaks for example make quite a racket, most owners refer to them as firecrackers sounds, but they can sound like knocking too. Exhaust leaks often aren’t overly expensive to fix. No need to guess, take it to the local auto repair shop and get a proper diagnosis. Then you’ll know for sure where you stand. Keep your fingers crossed for an exhaust leak … 
Running out of oil and a knocking engine is a common excuse to pick out a new car. An exhaust leak normally will not occur overnight and won’t prevent the engine from starting.