Catalytic Converter: Testing and Inspection

DIAGNOSTIC PROCEDURES
Either one of the following procedures may be used to diagnose a restricted catalytic converter:

Exhaust System Test at A.I.R. Pipe:

AIR PIPE METHOD
1. Remove the rubber hose at the exhaust manifold Air Injection Reaction (AIR) pipe check valve. Remove check valve.
2. Connect a fuel pump pressure gauge to a hose and nipple from a Propane Enrichment Device.
3. Insert the nipple into the exhaust manifold AIR pipe and follow the diagnostic procedure listed below.

Exhaust System Test at Oxygen Sensor:

02 SENSOR METHOD
1. Carefully remove Oxygen Sensor (O2S).
2. Install Exhaust Backpressure Tester in place of 02S.
3. After completing the diagnosis described below, be sure to coat threads of 02S with anti-seize compound prior to re-installation.

DIAGNOSIS
1. With the engine idling at normal operating temperature, observe the exhaust system back pressure reading on the gauge. The reading should not exceed 1.25 psi (8.6 kPa). Increase engine speed to 2000 rpm and observe gauge. The reading should not exceed 3 psi (20.7 kPa).
2. If the back pressure exceeds the given specifications, a restricted exhaust system is indicated.
3. Inspect the entire exhaust system for a collapsed pipe, heat distress, or possible internal muffler failure.
4. If there are no obvious reasons for the excessive backpressure, a restricted catalytic converter should be suspected, and replaced.