How to Troubleshoot a Catalytic Converter

The catalytic converter plays one of the most important roles in your vehicles emission system. It reduces harmful exhaust emissions by burning hydrocarbon (HC) and carbon monoxide (CO) into harmless gases. But after years of service, a catalytic converter may become rusty and plugged, considerably reducing engine power. The engine stalls frequently and is hard to start due to high exhaust back-pressure. Here we will follow some simple steps to troubleshoot two types of commonly used converters: monolithic-honeycomb shaped, and ceramic block-and pellet type. Then you will know whether you need to service or replace it. So, lets start.

Instructions

1

Locate the catalytic converter in your vehicle. It should be underside or at the front of the engine compartment. Follow the pipe coming out of the exhaust manifold until you see a stainless steel box screwed between the exhaust pipe and the muffler.

2

Make sure the engine is cold. If necessary, raise your vehicle with a jack and support it on jack stands in order to reach the converter.

3

Inspect the clamps, flanges and screws that attach the converter to the exhaust pipes. Make sure they are in good condition and replace rusted hardware as necessary. Check the converter case or outside shells; if they are corroded and in bad shape, replace the catalytic converter.

4

Hit the catalytic converter lightly using a rubber mallet. If you can hear a rattling sound, the ceramic block inside is broken and the converter needs replacement-this does not apply to pellet-type converters.

5

Connect a vacuum gauge to a main intake manifold vacuum source. Make sure to plug the vacuum hose disconnected from the intake manifold.

6

Set the transmission to Neutral-standard-or Park-automatic. Apply the emergency brakes; start the engine and let it idle for a couple of minutes. Ask an assistant to accelerate and maintain the engine at about 3000 rpm.

7

Watch the vacuum gauge. If the gauge needle drops 3 inches of Mercury (in-Hg)-for example 18 to 15 in-Hg-after engine acceleration, the exhaust is working properly. But if the gauge needle drops considerably, there is an obstruction in the exhaust system. Disconnect the muffler, exhaust pipe and catalytic converter, one at a time, and repeat the test. When the vacuum gauge registers a normal drop in vacuum pressure, you have found the restriction in the system.