cat backpressure
 

Howdy got a 98 civic lx code went of on cat. I replaced both up and downstream sensors. code still reapeared. I bought the little gadget that threads in before downstream sensor,it solved code light. I took of the exhaust manifold and visualy inspected the cat it looked ok to me. The car is gradually getting worse gas mileage as time goes on. Was 36 now down to 30 mpg. Could my problem be a lack of exhaust pressure? thanx...... Russ