Catalytic converters

[NoJiveMan]

Originally Posted by steel7

What are clear signs of a bad cat converter or one thats on its way out ? My cousin is a mechanic & i showed him my smog test results & he told me my cat conv is going out. My numbers were high (Measured 110, max is 111) on the HC (ppm). Besides for a cold hard start & rough idle the car runs good & idles nice with no back firing, etc. I did pass smog (barely) a few months ago. Ca has the toughest smog tests & laws in the nation.

Hope this helps a bit:
Catalytic Converter Diagnosis: Brake and Front End

A cold hard starting symptom is a indication of a different problem.
Rough idle indicates either flooding-loading up the cylinders with gas, defective plugs-plug wires, or other problems. Incorrect air-fuel mixture, if your vehicle has a carbureator, it could be as simple as a choke adjustment.

Ask yourself when was the last time you had a general maintenance tune up?

[tickyul]

Diagnosing a cat:
Backpressure test....check pressure reading just before cat.....should not be more than a couple of pounds(see specs for your model).
O2 sensor data.....upstream waveform should be switch between high and low voltage levels......downstream waveform should be basically flat.
Heat test......the converter is changing chemical energy into heat energy(other conversions take place to). You should see a heat rise when you check temps of the pipe going into the converter and then check the temp ON the converter....use a no-touch thermometer.
rubber mallet test(gently) tap the converter....listen for the sound of broken bits and pieces jangling around.

Of course, a good visual test will let you diagnose obvious problems such as a rusted, crushed or otherwise damaged cat.

[NoJiveMan]

Don't forget to check the air filter, it possibly the most overlooked thing on cars and trucks.

Automotive Service: Inspection, Maintenance, Repair - Tim Gilles - Google Books