85 s10 when I rev up my s10 it backfires what could this be I have duel ext from the muffler and a bigger cat that needs replaced but why does it backfire? its a 2.8L carb

Not O2, but could be restricted muffler full of old converter debris.

If you have a hih miles truck,it is very possoble you have aclogged cat.Have a muffler shop test pressure in front and behind by drilling small holes,checkin w/gauge,then welding back.This should be free if you replace the cat.

On most vehicles, the muffler is part of the cat-back exhaust assembly. Easily unbolts from the cat and pops out of the exhaust hangers.

your catalytic converter/s is/are plugged.
there is 2 of them coming out of both banks ( sides) of the motor. they join to one main pipe that goes to the muffler at the back of the vehicle.

you can take it to a muffler shop and they can test the pressure in your cat. converters for cheap or free. that will tell you if they are wrecked or not.

i would get it checked out asap because if your cats are the problem they well break your o2 sensors for the cats.

if you need to fix them you can do it cheeply by drilling holes in the cats to let the air out.

hope this helps

thats just what you need new muffler and ext with tip

FOR TRUE DUEL YOU HAVE TO HAVE TO O2 SENSORS AND TO CATS, OR YOU CAN DO ONE CAT AND OUT WITH TO PIPS AND THAT WILL WORK.

I suggest using a factory cat with a y-pipe behind the cat to your dual exhaust. LMC Truck makes a great bolt on duel exhaust with resonators. Easy to install and great sound.

a stock CAT will suffice. unless you want duel cat. than two stock. but a really good website with free shipping that i use for my s-15( gmc version s10) is autopartswarehouse.com and another Extremely good one is lmctrucks.com

You are correct. That portion of exhaust is indeed a catalytic convertor. This would be in the rear portion of the pipe with a flexible section that goes underneath the oil pan. Then you have a long muffler and a final muffler in the rear of the vehicle.

Nissan Scope Technician- 10+ years experience in Nissan dealership

Good Day,

Most aftermarket exhaust systems are cat-back. You defiantly need to keep the cat to comply with local emsisions regualtions. However you can remove the mufflers and replace them with high flow mufflers or resonators. Try to replace them with something not too loud so you are in accordance with noise laws in your area. I have a 2000 s10 with no mufflers, just a cat then a y-pipe to make it dual with two resonators coming straight out the back, I live in the states and made sure this sytem was 50 state street legal before I purchased it. I suggest you do the same to avoid harrasment by the police.

Good Luck

Hope this helps.