The best test to do in order to find out if your Chevy Astro van's catalytic converter is defective or not is the HC Reduction (Misfire Test) Test; but it requires a smog check machine or a 5 gas analyzer. A smog technician will heat up your Chevy Astro van's CAT for 3 minutes by running the engine at 2500 rpm, and than disconnect a spark plug wire and monitor how much reduction of HC the catalytic converter can handle in the next 10 seconds.
When a misfire occurs your Chevy Astro van's catalytic converter will release heat as it converters the unburned HC into water and CO2. This reaction will allow you to test the catalytic converter by creating a misfire and monitoring the HC reduction.
HOW TO PERFORM THE TEST:
1. Allow your Chevy Astro to run for several minutes at 2500 rpm after it is properly warmed up.
2. Disable one spark plug. Do NOT allow the engine or exhaust system to cool down as you do this. You can turn the engine off while disabling the spark plug, but this must be done and the engine restarted within 3 minutes.
3. Monitor the HC level as you disconnect the spark plug. The HC will increase dramatically for several seconds. Then, as the CAT heats up, the HC level should drop off significantly. Record the Peak HC level and the level that HC drops to as it gets hot.
A good catalytic converter will be able to reduce the HC emissions to about 50% or less of the peak HC emissions in just a few seconds.
THIS TEST MUST BE PERFORMED WITH CAUTION. DO NOT PERFORM THIS TEST FOR EXTENDED PERIODS OR UNDER A LOAD. A CATALYTIC CONVERTER CAN OVERHEAT TO THE POINT OF MELT-DOWN IN AS LITTLE AS 12 SECONDS IF ALL SPARK PLUGS ARE DISABLED WHILE UNDER LOAD.
An easy test (but less accurate) is a CAT temperature test which can be done at home using an inferred thermometer. You should keep your Chevy Astro van at 1500 rpm and monitor the exhaust pipe temperature at the CAT's inlet and outlet. You should see at least 40% increase in temperature at the outlet. This would indicate the CAT is relatively working ok.
