Hello, I recently bought a 2000 Honda civic dx on offer up for $2,800 with 120k miles in flamenco black and its a manual. It’s my first car and I’m very confused on what I should do, it needs a bit of work interior wise and under the hood. I understand it’s a honda and parts aren’t as hard to find nor expensive. I recently went to two nearby auto shops for a smog check to find out that it has no catalytic converter and two oxygen sensors are down. Whenever I start the car, I wouldn’t see a check engine light but turns out a fuse or something went out but it has a check engine light with the scanner tool they used. It’s also leaking a little oil. I knew from the very beginning that I’d put some money into it because it’d be a project car, but I’m wondering if all of this would be too much or if it’s really worth it. Before I bought the car I’d look at youtube videos of people transforming their civics from an absolutely totalled civic that wouldn’t even start, to selling it for$ 6-8k. I’d really appreciate any financial or mechanical advice on whether it’s worth fixing it up the cheapest way possible, or selling it to a junkyard. Thank you
I’m guessing a prior owner removed the cat, which turned on the check engine light, so they figured out a way to disable the check engine light. (This was a violation of US federal law btw.) When you purchase a car in the future, one thing to make sure you do it make sure the check engine light turns on with the key in “on” but before the engine is started. Then it should go out when the engine is started. It’s also a good idea to have your own mechanic inspect a used car (a pre-purchase inspection). I think you’ll be able to recover from this situation, Civics are pretty bullet-proof, so no worries, but if your locality requires emissions testing you’ll have to install a new cat, which might be a little pricey. I doubt the O2 sensors will need to be replaced. The missing cat is likely what was causing the codes for the O2 sensors.
I don’t see you making any big profits on this car, but you should be able to get it to daily-driver status without much $$ other than the cost to install a new cat. Suggest even though you’ve presumably already purchased it, first step, go ahead and pay a shop to do a pre-purchase inspection. That will cost about $100 or so, but will be well worth it for the info you gain.
If your goal is to flip the car for a profit, and you’re needing to get it diagnosed by two separate shops, then you should sell it now and not try this again until you’ve learned a lot about working on cars. Flipping cars for profit only works if you do all the work on them, otherwise all your profits get eaten up paying mechanics.
If your goal is to have a 2000 Civic that’s modified to your liking so that you can drive it, then we can explore more about whether or not this particular one is worth doing that to.
If it runs well, is in decent condition, and that oil leak is easily repairable or just a seep that can be ignored, I’d have a shop install an aftermarket converter and it should be fine. If you’re intending to resell it, just pass it off on the next sucker as is. I used to flip vehicles as a hobby. Sometimes I’d make a thousand or two bucks, sometimes I’d lose a couple of hundred, and sometimes I’d just break even. I mainly just enjoyed tinkering with them. And if you can drive one 10k miles and sell it for a profit, break even, or even lose a few hundred bucks…well, it beats the heck out of a car payment. My current truck I didn’t buy with intentions of flipping, but I figured I could. I’ve put about 40k miles on it over 2 years. Installed new tires and a few other things. Maybe $1k in parts, tires included. A guy offered me $2500 over what I paid for it recently. The flipper inside is tempted 
The converter and O2 sensors would not be a big deal IMO. The oil leak may or may not be; especially if it’s a rear main seal leak (engine or trans has to come out) or if the engine is leaking because it’s flat worn out.
If it were me, I would run a compression test both dry and wet.
If the test results were bad then I would try to sell it as is.
Keep in mind that if the engine is blowing through oil that could be the reason for the converter/O2s missing. Clogged and killed…
There is also the unknown CEL. The CEL is out because someone likely disabled it; removed the bulb, cut the wire to the ECM, or whatever. Replace the converter, O2s, repair the CEL, and then what if more codes start appearing with no end in sight?
As for TV or Youtube videos you really need to take a lot of those with a grain of salt.
No selling to a junkyard at this point. The boneyard will be hundreds of dollars at best and you are already into it for 2800 so do not go that route.
True, scrap value is a couple of hundred or so. And the converter that is worth more in scrap value than the car is already gone!