A clogged or stopped-up converter will affect the performance of the vehicle's engine. Partially clogged will reduce power because the exhaust system is not being allowed to breathe properly. A completely clogged converter will prevent the engine from running. It may start up, but once the back pressure of the exhaust builds up between the manifold and throttle, it will choke itself out. Any quick fix to allow the vehicle to run should be considered a temporary solution to a bigger problem.
The quickest temporary solution is to remove the front oxygen sensor. This will create an exhaust leak before the back pressure builds up against the clogged converter. An exhaust leak is loud and everyone is going to know that you have a problem with your car the second you start it. It will be louder upon acceleration. Windows in your vehicle should be rolled down to prevent carbon monoxide and other harmful pollutants from contaminating the air inside the passenger cab. This fix should only be done to get the car from point A to point B -- point B being the repair station to have the catalytic converter replaced.
To prevent an exhaust leak from occurring, another alternative is to remove the converter, hollow it out if capable of doing so, and then replacing it. Another would be to apply a piece of flex or straight pipe in the place of the catalytic converter. This is a highly illegal practice that most every reputable repair facility will refuse to perform because of liability. And again, this type of quick repair should be considered only temporary to get the vehicle from where it is to the repair station.
The Computer and Emissions
Today's vehicles are designed to run with catalytic converters and bypassing them, even temporarily, will affect the performance of the engine and can cause further damage to other components. Oxygen sensors are set in place upstream and downstream in the exhaust system to monitor fuel-to-air ratio from the throttle and to also monitor the catalyst efficiency. When the oxygen sensor cannot perform its intended purpose, it will trigger the check engine light to illuminate. In addition, the intense heat from a clogged converter can easily damage the upstream sensor. When the upstream sensor cannot communicate its data to the engine control module, the computer is unable to make the necessary adjustments for the perfect fuel-to-air ratio to decrease emissions. Unburned fuel can bypass the throttle in a rich (too much gas) fuel case or too much air can cause a lean fuel case, where the engine may chug, buck and even stall.
A temporary or quick fix to a clogged converter should be rectified as early as possible to prevent damage to other components and to abide by government laws that mandate catalytic converters on vehicles that came with them originally.
Catalytic converters do not necessarily clog due to age or failure on their own. A poor-performing engine, leaded fuel or an oxygen sensor failure can contribute to the decline and demise of the catalytic converter. Replacing the converter may help the exhaust breathe for the time being, but if the vehicle is not properly diagnosed, the new converter's longevity will be compromised.
Direct-Fit Versus Universal
There are two common types of replacement converters and both have their benefits and drawbacks. Direct-fit converters are designed to fit the vehicle as the original converter did. This application will come with the necessary flanges, pipe extensions and any other features to allow you to remove the old converter and replace it with one in the same manner. Direct-fit are more costly, but will save you installation time or save you money in labour because a professional doesn't have to install it.
Universal converters are much cheaper, but they're often nothing more than just the converter itself. In other words, it will not come with flanges, pipe extensions or any necessary features to remove the old converter and install the universal one in its place. Universal simply save you money on the price of the converter, but you will undoubtedly have to invest more time or more money to make the converter fit to your exhaust system. In some cases, welding or having pipe extensions made by muffler shops will be required. Overall, consider the benefit of the direct-fit converter to save yourself the time and hassle of trying to install the universal.