1993 Chevy Corsica Ignition or brakes

I got a 93 corsica 3.1L multiport V6 and it has 260kmi on it, and I got it cheap (really cheap)
anyway it doesn't start, pulled the air box and found oil+gas sitting in a small puddle, anyway when I go to start it, it occassionally backfires in the intake only never an exhaust backfire always in the same cylinder the others don't fire, checked spark and found that only one spark plug fires but it keeps moving to which spark plug fires (btw it has a very very strong spark, while two have weak sparks, one is weak and intermittant and two don't fire ever)
When I first purchased the vehicle I was told it needed a timing chain which turned out to be false
but now I wonder ive been told to replace the modules (which I am willing to do) but if is the master computer (the ignition trigger signal) then the car is porbably just junk (too expensive for me)
otherwise could the brake booster diaphragm be blown and how to test for that without a running engine.