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.