Catalytic Converter: Testing and Inspection

Symptoms of a faulty catalytic converter are:
^ Poor power output
^ Idle speed drops
^ Engine stalls
^ Rattle in the exhaust

The converter can be damaged by:
^ Engine misfiring (bad spark plugs, ignition wires, connections, etc.)
^ Ignition timing out of adjustment
^ Straining engine (pulling a trailer, mountain driving, etc.)
^ High speed driving at high outside temperatures.

THE CATALYTIC CONVERTER CAN BE CHECKED IN SEVERAL WAYS

VISUAL INSPECTION
- Visually inspect exterior of converter.

^ If severe damage is noted, such as dented, crushed or rusted out shell, replace converter.

- Whenever converter is removed from vehicle, check ceramic element through exhaust inlet and outlet.

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

FUNCTIONAL TEST
- Run the engine at 2,500 rpm for approximately 2 minutes to heat catalytic converter to operating temperature.
- Connect a surface temperature probe on exhaust inlet of catalytic converter and measure temperature.
- Connect surface temperature probe on exhaust outlet of catalytic converter and measure temperature.

^ Outlet should be at least 100°F (38°C) hotter than inlet.

- If temperature differential is less than specified, catalytic converter should be replaced.

EXHAUST RESTRICTION CHECKS:

MANIFOLD VACUUM TEST
- Connect vacuum gauge to manifold vacuum source.
- Start engine and idle.

^ Note vacuum reading, and record.

- Run engine at approx. 2,000 rpm with no load. Note vacuum at steady engine speed.

^ If vacuum is less than previous (idle) reading by greater than 75mm Hg (3" Hg), a restricted exhaust system is indicated.

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

EXHAUST PRESSURE CHECK AT OXYGEN SENSOR OR CO TEST PIPE
- Install exhaust backpressure tester in place of Oxygen sensor (or CO test pipe).
- With engine idling at normal operating temperature;

^ Gauge reading should not exceed 8.6 kPa (1.25 psi).

- Increase engine speed to 2000 rpm.

^ Gauge reading should not exceed 20.7 kPa (3 psi).

- If backpressure at either speed exceeds specification, a restricted exhaust system is indicated.
- Inspect exhaust system for a collapsed pipe, heat distress or possible internal muffler failure.
- If no obvious reasons for excessive exhaust system backpressure are found, suspect a restricted catalytic converter.
- After completing test, coat threads of oxygen sensor (if removed) with anti-seize compound prior to reinstallation.

DROP TEST
- Remove converter from the car.
- Hold the converter vertically and drop it from about 20 cm (8 in) on to a block of wood.
- Turn the converter over and drop it on its other flange from the same distance.
- If a slight knocking sound is heard from inside the converter, or if the ceramic grid moves inside the housing, the converter is damaged and should be replaced.