89 civic started a light fire!!

as i was driving for about 2 hours, my car just suddenly felt like it was running out of gas when really it was on half a tank a little "popping" noise happened aswell...and my CHECK ENGINE light came on and i couldnt go as fast as i could, it felt like something was cloged in the pipe and was having a hard time to drive...i went to gas station and filled it up, still the same.
as i was 10 min away from my house i notice smoke starts cpmmin from the bottom..i pull over quickly and notice a LITTLE FIRE is starting(around the CAT)..cuasing a slight burn in my interior!

-my car can still start,

-put brand new distributor,rotor,spark plugs & wires and a whole new aftermarket exhaust right after the CAT..new aftermarket headers aswell..(3 months ago)
-i put fuel injector cleaner as well..nothing happens

*the small backfiring happenes where the upper and lower header connects.

*alot of smoke comes from my exhaust causing the bad smell

WHAT COULD POSSIBLY BE WRONG TO MY CAR AN DHOW MUCH IS IT GOING TO COST ME ?!

you may have a clogged cat. and if you are running a little rich, it could be dumping gas into the exhaust system. the extreme heat from the cat in correlation to a fuel source could have started the fire. I've seen this happen before, the cat got so hot, it was glowing red. This is just a wild guess. this could also cause that sudden loss of power because of too much back pressure. Could be as easy as putting in strait pipe in place of cat. did mine for around 10 bucks. of course welding was needed.
hope this helps.

Come on man, you replaced everything in the exhaust system except for one component and you mentioned it twice. The "backfiring" is happening because the exhaust gases are building up and looking for a place to go, luckily enough, they have nifty bolts with springs on them that hold your header to your CAT in case this happens.

The answer is only obvious: Apparently your getting exhaust through your header because its backfiring from there, but the car is still acting like something is clogged up in it. You replaced the exhaust system after the CAT so that should be all nice and clear...whats left?

clogged cat sounds logical. bad o2 sensor too.

Bad O2 would cause the car to run rich, but it wouldn't cause it to bog down like something is clogging it and it to backfire at the joint where it connects to the Cat.

gonna fix the car this weekend..
also found out my car is running on only 1 and 4th cylinder..should i buy the spark plugs first before taking out the CAT?

Replace the CAT and go from there

oh cripes....