A properly working cat, no. Removing it, no. A failed cat, yes.
A properly working cat, no. Removing it, no. A failed cat, yes.
A properly working cat, no. Removing it, no. A failed cat, yes.
the same as any cat, you usually plug them up with cheep gas and fuel additives.
A bad catalyic converter will do a lot to diminish your gas milage. You might also have issues related to a "tune up" that include timing, a dirty air filter, dirty/worn spark plugs and other things.
It could, yes.
no
No
No, I don't think they would negatively effect your gas milage. You just need to make sure that you keep them with plenty of air. That is what would negatively effect your gas mileage.
yes
If it is malfunctioning it can affect fuel mileage.
Roof racks themselves have a negligible effect on gas mileage.
Yes.Yes.
Should have no effect
No, there are many other parts on the engine that can affect mileage but the catalytic converter is a passive device and, if new and clean, cannot affect the way the engine runs or the mileage it gets. Think of it as a filter, althought it's actually a lot more complex than that, if it lets the exhaust gases flow throught without any major obstruction then it can have no effect on the car's performance.