It was cool and dry this morning and the car ran perfect. No shuddering up hills and when I started it up this morning it never missed a beat.

I had a 96 Firebird Formula a few years ago and it throw similar codes and the dealership replaced all the O2 sensors at a cost of nearly $1000. A week later the codes were back and after 2 weeks of gripping with the I told them to just replace the air pump and it fixed the problem. This episode made me very skeptical of "bad O2 sensor" diagnosis.

How can you test the Cat to see if it'* plugged? Is it very expensive? Does the 2000 SSEi have an air pump? I don't want to be a parts changer but if the Cat is pretty cheap would it be worth replacing?

When my cat was clogged, it definately ran worse when the car was hot.. As far as i know, there is no way to really "test" to see if the cat is clogged. Your best starting point would be replacing your O2 sensors.. Do it yourself, if you can.. its not that difficult. And as fdar as i know, SSEis didnt come with air-pumps, but california emissions SEs and SLEs did.

The fact that you are feeling like the car might stall upon start up may be a good indication of a non-catalytic problem

You can "test" the cat by shaking it. If it rattles, that'* typically an indication that it'* bad.

If you want to perform the test when the car is hot, use a broom handle to agitate the cat converter.

yes, if the cat rattles its bad, but keep in mind that this is not a scientific approach to diagnostic, and can easily lead to an inaccurate result

Testing for a rattling cat may not be scientific, neither are many other automotive diagnostic tests.

Start with the rattle test, a broom handle etc work fine. (we know what Mark has handy in his garage ). If that doesn't yield any results, then it is possible to have your exhaust backpressure tested and that is the proper way to test a catalytic for possibly being clogged.

While neither of these tests are scientific, both can be effective to diagnose a bad catalytic.

Toasty....are you pulling out the chemistry set to test the exhaust? (j/k)

no, i just wanted to clarify that the result of the bang test may not be directly related to the condition of the cat

If the Cat shows no sign of being plugged and the SSEi has no airpump what else besides the O2 sensors could it be?

If I pull the O2 sensors, which looks to be a pretty easy job, how could I tell if they are bad? Is there some kind of resistance test I could do? What are some visual signs of a bad O2 sensor? Are there only 2 O2 sensors? If the "up stream" O2 is bad will it automatically make the "down stream" O2 throw a similar code?

I know you guys are probably tired of talking about it but I just know if I take it to the dealership they are going to get the O2 sensor codes and want to replace them. I have nothing against that but if it doesn't fix it I just might go off the deep end. In my experience dealerships are typically parts changers and you can wind up knee deep in money and BS before you know it and the car is still broke.

We aren't tired of helping out. We are just beginning.

The best test I know of for an O2 is to watch the O2 on a scanner. At idle you should see the O2 toggling rich/lean or if you watch the voltage you should see toggling between say the 100-300 range and the 700-900 range. The lower and higher the toggling and the quicker it toggles..the better.

Ok then here'* the story. Dad is a Matco dealer and has access to the hand held scanners that they sell. He had a new on on the truck last weekend and sunday after noon we plugged it in and played around with it. Now he nows how to demo the unit but when it comes to dignosing the car we were guessing. I threw the O2 sensor codes and offers a test. We ran the test as you describe and the O2'* sensors responded in the range of the test. The range as I remember were 100mv to 1 volt or so. So yes the O2'* passed according to the hand held scanner we used.

So we cleared the codes and the SES light was off until Monday when I was coming home from work. I went to pass a car and the light came back on as I went more or less WOT. The car runs worse after you clear the codes but gets better when the SES is tripped. I assuume because the computer is adjusting it'* parameters to off set the codes.

Ahhh good information.

During the test were you able to see the voltage go up and down rather quickly? It sounds like while the sensors passed the test, maybe they are hanging on the low end for too long at times. And when at WOT, that sensor is going to be darn close to a full volt.