I have a 1992 Full size Blazer. I have A hole in the Exhaust system and a bad muffler. I just got the truck in Oct of 08, it has 98,000 on it. When i start it, it runs fine, but after it warms up, it begins to backfire, and idles rough. i replaced the fuel filter already. I dont know how long its been since its been tuned up. I also dont want to just start dumping money into unnecessary parts that i dont need right now. Please Help!!!!!!!!!! thanks

 

The hole in the exhaust does not happen to be before the O2 sensor does it?

 

to be honest i dont know, i know there is a hole in the pipe by the muffler, it could be a hole some where else lol, i know for a fact that no exhaust comes out of the muffler.

 

Find where the exhaust leak is. If it's before the O2 sensor right after the exhaust manifolds then it's causing your engine to run rich which throws fuel into your exhaust causing it to explode upon contact of the hot pipes (backfire).

 

if it has a hole, do i just need a new exhaust system, This truck is new to me so, i want to know what i need to replace first. Thanks for all of your help

 

You will likely need to replace the exhaust system on it if it is badly rotted.

Another typical spot is the throttle body base gasket.

 

Sounds like your cat is pluged up. It usually starts acting up when it reaches operating temperture. Even though its low mileage, it's still a '92. Take the cat off and inspect it. Look through it toward the sun. If you can barely see through it, its probably good.

You can run it with out a cat to see if the symtoms persists. Also check the EGR, a clogged EGR will cause it run rough but not backfire.