If I took off the catalytic converter, will it make my fuel get better mileage?
Don't listen to the naysayers. A engine is a pump, anything you do to increase pump efficiency, is going to increase gas mileage. A new cat will not rais fuel consumption much, But if it has over 100,000 miles on it, You will see a marked increase or “restoration” of gas milage. This is especially true of cars with a secondary air pump. They are not exactly filtering the air, before its pumped into you exhaust.This is what gets fun. If you reprogram, or modify the O2 sensors signal to bring the engine to stylometric fuel ratio or just less, you will get a 5–10% increase in gas milage. This trick really shines in stop and go traffic. If you analyse the wave form of the upstream O2 sensors, you will notice it spends a lot more time rich, than lean. You are sitting at red lights feeding that Fat Cat, so it can make more smoke.All cars are set up to fuel that catalytic convert. This keeps them hot and working. Without extra fuel pumped thru the engine, that cat has nothing to do, cools down, and slowly plugs up. To bad your cat will plug up if you lean out the engine. Hint, Hint……….