Catalytic Converter: Testing and Inspection

FAULTY CONVERTER SYMPTOMS
^ Poor power output
^ Idle speed drops
^ Engine stalls
^ Rattle in the exhaust

POSSIBLE CAUSES OF CONVERTER DAMAGE
^ 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.
^ Using leaded or high sulfur fuel.

CONVERTER INSPECTION AND TESTING

Visual Inspection

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, check ceramic element through exhaust inlet and outlet. If element is clogged, melted or otherwise damaged, replace 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. Outlet should be at least 100°F (38° C) hotter than inlet.
4. If temperature differential is less than specified, catalytic converter should be replaced.

Exhaust Restriction Checks

Manifold Vacuum Test
1. Connect vacuum gauge to manifold vacuum source.
2. Start engine and idle. Note vacuum reading, and record.
3. 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 3" Hg (75 mmHg), a restricted exhaust system is indicated.

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

Exhaust Pressure Method At Oxygen Sensor Or CO Test Pipe
1. Install exhaust backpressure tester in place of Oxygen sensor (or CO test pipe).
. With engine idling at normal operating temperature, the gauge reading should not exceed 1.25 psi (8.6 kPa).
3. Increase engine speed to 2000 rpm. Gauge reading should not exceed 3 psi (20.7 kPa).
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.

Drop Test

1. Remove converter from vehicle.
a. Hold converter vertically and drop from about 8 in (20 cm) onto a block of wood.
b. Turn converter over and drop on its other flange from same distance.
c. If a slight knocking sound is heard from converter, or if ceramic grid moves inside housing, converter is damaged and should be replaced.