what are some common problems that occur when you have an exhaust leak

how does your gas mileage suffer

 

One thing I have heard that an exhaust leak does is make it so the sound comming from your muffler is quieter... which is why I need to patch up mine right quick! I wanna sound fast while I rev in my driveway... at least till I get the car on the road :P

 

loss of power, more noise, backfires, and I don't know if it would effect gas mileage at all.

 

Any sure way on how to spot exhaust leaks?

 

my exhaust leak is comming from under the heat-sheild of the main cat. does this make it any better or worse?