Write an article based on this "Check for exhaust leaks. Measure back-pressure in the exhaust system. Perform a mallet test for old converters. Consider more advanced tests."
Once you've installed a new catalytic converter, one thing you'll want to do immediately is double-check to make sure there aren't any leaks in the exhaust system on either side of it. Depending on where it is, an exhaust leak can cause a variety of problems for your vehicle, including reduced fuel efficiency and long-term damage. There are several ways to find an exhaust leak. One is to simply be observant while you drive — if your car sounds louder than normal when it runs or seems to "rumble" more, you may have a leak. You can also check for leaks by jacking your car up, starting it in park, and carefully moving a lit candle along the length of the exhaust tubing. Leaks which are invisible to the eye should cause the flame to waver or blow out. One problem that can occur in faulty catalytic converters is that they can become "backed up" with soot, debris, and other exhaust byproducts or broken apart inside the converter. In this case, the engine's ability to rid itself of exhaust is hampered, which can cause a vehicle's fuel efficiency to plummet and can even cause the engine to stall in severe cases. Luckily, performing a backpressure test is simple — just screw a pressure gauge into the oxygen sensor's hole before the converter in the exhaust manifold in most vehicles. The pressure reading should be less than 1.25 psi when the vehicle's engine is running at 2,000 RPMs. The worse the congestion is, the higher the pressure reading can be. Very bad backpressure readings can approach 3 psi. If your car's converter is old and worn, one simple test can tell whether it needs to be replaced very quickly. Simply grab a rubber mallet (or similar tool) and give the converter a firm hit. If you hear any sort of rattling, your converter needs to be replaced — this indicates that the metallic catalyst within has begun to corrode and crumble.  However, if you don't hear a rattle, this doesn't necessarily mean that your converter works well. There may still be other problems with it. To be clear, this test can only tell you if you have a bad converter, not if you have a good one. Catalytic converters can be tricky parts — if you're in doubt about whether or not yours is functioning properly even after performing the tests above, don't hesitate to take it to a mechanic or specialist. These professionals will have access to the type of equipment that can be used to perform more advanced tests, like delta temperature tests, oxygen storage tests, and CO2 tests.  Most auto shops that offer smog testing will be able to perform these sorts of emissions tests.