How to Test your Catalytic Converters

[sperold]

Heard something new today and want to see if anyone has heard of this before.
Been trying to get through an emission test, and finally took it to a shop that is kind of chatty. After the car failed, the owner told me how to determine if converters were my problem. You take your car to a shop that has a "heat gun", a handheld gun like thing that places a red dot on the target you want to know the temperature of. I took it to a little rural shop where they took the temperature of the engine down pipe, the converter, and the pipe right after the converter.
The conventional wisdom is the converter should be nearly the same temperature as the downpipe.
My downpipes were 600ish, my converters were 300. Bad converters.
The proof will be when I install the new system and retest, but I am going with this as gospel for now.

 

[itwonder]

You can also buy back-pressure gauge kits for testing catalytic converters.

 

[sperold]

How does that work?
The reason I am so interested is...... the car passed the etest 2 years ago with flying colours, and I never had a check engine light during that time for anything, and I run the car for 120 miles at a time every week.
Then I have an 89 (6 years older) that passed with no assistance, after sitting around for half a year, after being driven only in the winter, on short trips.
I am baffled.

 

[hawkeye18]

cats should be quite a bit hotter than the rest of the exhaust... for some reason 900° comes to mind. If they're only 300, then they're definitely not working right.

 

[luigisho]

I think typical cats operate around 550 degrees.

 

[makachana]

I go with itwonder, the only true way to see if cats are plugged is with the back-pressure gauge. It's what we use in our shop to test for plugged cats.

 

[makachana]

Sperold, this may help you a bit to understand cats, give it a read.

http://www.aa1car.com/library/converter.htm

 

[raff18]

When we test to see if a cat is working we look to see if the cat is hotter on the out at least 30 hotter if it's colder on the out then it's no good