I was wondering if there was anyway to check if a catalytic converter was clogged other than just replacing it or taking it off. I heard from a shop that if you hit it and it makes noise like theres something inside of it then it is clogged. I tried this and it made the noise but then I tried it on my moms brand new car and it made the noise to so now Im kinda thinking that they all make this noise. Is there anyway to check the compression of the cylinders and tell or anything like that. I have been getting really bad gas mileage (like 12city/16hwy with my 2.3l 5-spd) and have been trying everything to get it to get better gas mileage. I also noticed on my air filter there are two outlets for emission hoses and mine only has one attached and I cant find the other one. Would this make a big diffrence on mpg. thank you guys for your help