Catalytic Converter: Testing and Inspection

Chart B-1, Restricted Exhaust System Check:

EXHAUST BACKPRESSURE CHECK (CHART B-1)

VACUUM GAUGE TEST
Engine at normal operating temperature:
- Connect a vacuum gauge to any convenient vacuum port on intake manifold.
- Run engine at 1000 rpm and record vacuum reading.
- Increase rpm slowly to 2500 rpm. Note vacuum reading at a steady 2500 rpm
- If vacuum at 2500 rpm decreases more than 3" Hg, from reading at 1000 rpm, the exhaust system should be inspected for restrictions
- Disconnect exhaust pipe from engine and repeat Step 2 & 3. If vacuum still drops more than 3" Hg, with exhaust disconnected, check for exhaust manifold restriction and valve timing.

THERMAL TEST
Use a pyrometer to measure the temperature difference between the inlet and outlet. A warm and properly working catalytic converter will show about 100 degrees hotter at the outlet.

NOTE: The computer system also monitors the catalyst condition by comparing the response rate of the oxygen sensors in front and behind the right side catalytic converter. If the catalyst is working properly, the rear oxygen sensor should show far less activity than the front sensor. If the converter is not working efficiently, a diagnostic trouble code P0420 should be stored.