Catalytic Converter Testing for Poor Performance and Suspected Clogged Catalytic Converter 

A Catalytic Converter needs to pass 2 tests to be good.  The first, and most obvious is the ability to change Pollution into Friendly Gases.  For the most part, this test is performed during state emission testing. 

The Second is to check for restrictions in the Catalytic Converter.  Restrictions can be caused by excessive Oil Blow By, Antifreeze leakage into a cylinder ,Unburnt fuel from a Rich Fuel Mixture condition or Over Temperature from a Too Lean Fuel Mixture.  Before replacing the Catalytic Converters, run this simple test to verify their condition.

A Major European Auto Manufacturer has already outlined the test to check for restriction. 

1. Remove the Pre-catalytic converter Oxygen Sensor.
2. Install the adapter into the exhaust pipe, Do Not Over tighten, past snug.
3. Install the Pre-Catalytic converter Oxygen Sensor into the adapter.
3. Run a 6' hose from the adapter to a pressure gauge.  I use the Old Style Manifold Vacuum Gauge that can also measure pressures up to 10 PSI.
4. Start the engine and briefly raise the RPM to 2500.  With the engine speed stabilized at 2500 RPM, the pressure measured on the gauge must be below 1.5 PSI

A restricted Catalytic Converter will measure greater than 2 PSI

In real life, my 1995 740i read almost Zero on each Catalytic Converter, the needle barely moved.  

Machined of Plated Steel, with integral Crush Gasket and a Brass hose fitting.  

This is the only Catalytic Converter Test method that keeps the Oxygen Sensor in operation while measuring the Restriction in the Catalytic Converter.

I am selling the Catalytic Converter Adapter for $20.00 for testing Catalytic Converters.  The kit includes the adapter, instructions, and shipping in the Continental USA.

Please mail questions to

Tom at

The picture below shows The end of the Catalitic Converter that screws into the exhaust pipe ahead of the Catalitic Converter and the pressure connection to the pressure gauge.


The design of the Catalytic Converter Adapter is proprietary.  An application has been made to the US Patent Office.  All Rights Reserved.
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