Catalytic Converter: Testing and Inspection

VISUAL INSPECTION
A partially restricted or blocked exhaust system usually results in a loss of power or backfire up through the throttle body. Verify that the condition is not caused by ignition or fuel system problems, then perform a visual inspection of the exhaust system. If the condition cannot be located by visual inspection, perform the following procedure.

1. Visually inspect exterior of converter. If severe damage is noted, such as dented, crushed or rusted out shell, replace converter.
2. Whenever converter is removed from vehicle, Shine a light through the outlet, observe through the converter to determine if the converter is plugged by carbon buildup or lead contamination.
3. Gently shake the catalytic converter and listen for signs of loose components.

If the element is clogged, melted or otherwise damaged, replace the converter.

FUNCTIONAL TEST
1. Run the engine at 2,500 rpm for approximately 2 minutes to heat catalytic converter to operating temperature.
2. Connect a surface temperature probe on exhaust inlet of catalytic converter and measure temperature.
3. Connect surface temperature probe on exhaust outlet of catalytic converter and measure temperature.
4. There should be at least 38°C (100°F) increase in temperature from the inlet to the outlet.
5. If temperature differential is less than specified, catalytic converter should be replaced.

EXHAUST RESTRICTION TESTING

Exhaust System Back Pressure Check (Using Oxygen Sensor Mounting Hole):

Exhaust Pressure Method At Oxygen Sensor
1. Install exhaust backpressure tester in place of oxygen sensor. If there are two oxygen sensors use the one ahead of the converter.
2. With engine idling at normal operating temperature, the gauge reading should not exceed 8.6 kPa (1.25 psi).
3. Increase engine speed to 2000 rpm. Gauge reading should not exceed 20.7 kPa (3 psi).
4. If backpressure at either speed exceeds specification, a restricted exhaust system is indicated.
5. Inspect exhaust system for a collapsed pipe, heat distress or possible internal muffler failure.
6. If no obvious reasons for excessive exhaust system backpressure are found, suspect a restricted catalytic converter.
7. After completing test, coat threads of oxygen sensor with anti-seize compound prior to reinstallation.

Vacuum Gauge Method
1. Attach a vacuum gauge to an intake manifold vacuum source.
2. Connect a tachometer, following the manufacturers directions.
3. Start the engine and observe the vacuum gauge. The gauge should indicate a vacuum of 16-21 inches Hg.
4. Increase the engine speed to 2000 rpm and observe the vacuum gauge. The vacuum will decrease when the speed is increased rapidly, but should stabilize at 16-21 inches Hg and remain constant. If the vacuum remains below 16 inches Hg, the exhaust system is restricted or blocked. Stop the engine and proceed to the next step.
5. Disconnect the exhaust pipe at the manifold.
6. Start the engine and increase the speed to 2000 rpm. Observe the vacuum gauge.
7. If the vacuum stabilizes at 16-21 inches Hg, restriction or blockage is either in the exhaust pipe, catalytic converter, muffler or tail pipe.
8. If the vacuum stabilizes below 16 inches Hg with the exhaust pipe disconnected, the exhaust manifold is restricted.
9. Stop the engine, connect the exhaust pipe and remove the muffler. Start the engine and increase the engine speed to 2000 rpm. Observe the vacuum gauge.
10. If the vacuum stabilizes below 16 inches Hg, the restriction is in the catalytic converter.
NOTE: In the event of a catalytic converter failure, always inspect the muffler and ensure converter debris has not entered the muffler.
11. If the vacuum is normal, the muffler or tail pipe is restricted.
12. Stop the engine.
13. Disconnect the tachometer and vacuum gauge.