One of the signs of a plugged catalytic converter is a serious loss of performance when the engine is warm. Although your car engine may start and run completely normally when cold, if there is a performance loss when the engine is warm or under hard acceleration, the first thing to troubleshoot is the catalytic converter. You'll need a little bit of car know-how and a relatively inexpensive piece of equipment to get the job done right.
Open the hood of your car.
Locate a vacuum hose. The easiest one to find will be a hose that leads from the engine intake manifold to the power-brake unit. It will be rubberized, black, and the only hose that leads from the engine to the power-brake unit.
Remove the vacuum hose from the power-brake unit. It may be a simple as pulling it off a connector, or there may be a clamp holding it on. The clamp can be removed by using a flat-blade screwdriver and unscrewing the clamp nut in a counterclockwise direction. When the clamp is sufficiently loosened, pull the hose off the power-brake unit.
Attach the vacuum-gauge tester to the power-brake vacuum hose by first locating the correct adapter that comes with the vacuum gauge and plugging it into the vacuum-gauge hose. Next, plug the other end of the adapter into the power-brake unit vacuum hose.
Start the vehicle.
Check the vacuum gauge when the vehicle is running. Leave the vehicle at idle and allow it to fully warm up. As the vehicle warms to normal operating temperature, the vacuum pressure reading will gradually drop if there is a clogged catalytic converter.
