Has he been checked by a vet to rule out any physical problems?

Are both cats neutered? If not, this might help.

How many litterboxes do you have? Two might be a good idea.

How often do you clean the litterbox(es)? At least once a day is
recommended.

Which kind of litter do you use? Maybe Simba doesn't like it...

Camilla

you shouldn't have gotten another cat if you cant be bothered looking
after it.. since this one was born in a sad situation, it's probably
got some bad habits..  you just need to take some time and train it,
not give it up the minute it does something you dont like

a few ideas to consider
am just guessing these are 2 male cats
1 male and 1 female, is not such a big help
cats are territorial. Scent marking is common for their species.

do you know your cat thinks you are a big cat?
so when you have litter box training problems

bring the litter box into your bathroom, and do not jam the box into a
corner.
6 inches to the wall improves their aim.

get a very good clumping litter, for the starter learning lessons.
never get scented

i have 3 female cats. they visit the bathroom with me every morning.
they kinda line up to get some attention, and they enjoy the personal play
time.

nothing in this world is automqatic
cats always prefer to be clean if they can.

now here is a good thought
move down to the litter box about 4 to 6 inches from it.
your catsa nose about there.

if yoyu tend to pass out from the fumes, then why would you call the cat bad
cat.

NOW maybe is a good time to have some good interactions with the cat.

reply if you find the ideas of use or not to you.
info is a good idea. gender, helps. do you know white haired cats tend to
have poor vision problems.
is the litter box lite up 24 hours a day, or is it in a dark corner.
what happens to you if you have to go to the bathroom in a dark room?

well, you have a few ideas towork on.

Well scent is a part of a cats language. It might be sick or it might be
saying that its not happy with the newcomer in the house. Probably the cat
is stressed.

Take the cat to the vet to make sure nothing is psyically wrong with it.

Get multiple litterboxes. Clean them _every_ day.

Clean the places where is has left its droppings with an unperfumed soap
that removes smell.

Dont tell the cat off for doing it or dip its nose in it - as this will make
the problem even worse.

Have both cats neutered.

Make sure you have time for them both every day. For eksample set aside a
half hour every day at approximately the same time where you sit down and do
nothing but play with them - especially the one with the problem.

Buy Karen Pryors book about clickertraining cats as it provides usefull
methods to train cats to stop doing things like that. Train the cat to leave
its business in the litterbox and give it praise and a snack every time it
does it. Soon the cat will stick to the litterbox to get your attention and
praise.

Realize that its not the cats fault - but YOURS. And that you can eliminate
this behaviour with time and efford. Probably its doing it, because you got
a 2nd cat in the house. Cats aren't dogs, you cant allways expect to them to
be happy with new cats in the house. Maybe you should consider finding a new
home for the 2nd cat?

Hopefully you will follow the above advices and with training and efford
you'll manage to soon eliminate the behaviour. Good luck!

/Gainsbourg