OT:exhaust temp

[joeb]

my other car gave me a code that reads "cat conv efficency". I think that most cats raise the exhaust temp. i have a car with a main cat that has dual inputs/single out. the inlet pipe temp is 380F and the cat outlet is 280F. would the larger area of the dual style cat result in a pressure drop which would result in a lower temp? i would think the cat outlet should be a higher temp. maybe i should try and measure my STS and see what temp readings I get, inlet/outlet. any thoughts on this? BTW, both inlet pipes on my other car read the same temp so i figure the manifold cats are ok.

[JasonA]

Exhaust temperature varies GREATLY while driving, so I don't know how easy it would be to get a repeatable temperature measurement.

Perhaps the "cat conv efficiency" code is simply stating that when the computer compares the output from the O2 sensors in front of and behind the converter, it's not seeing what it's expecting?

[joeb]

I threw in the temps as a basis for discussion. I did some searching on the internet and found that a proper internal operating temp for a cat is 1200-1400F. a motor that is running too rich might dump gas in the exhaust and the cat could get up to 2200F. that is why the cats burn out on a poor running car. I just am puzzled why my outlet temp is lower than the inlet. i am going to check my STS this weekend.

[JasonA]

Perhaps, as you were surmising up front, the converter is no longer effective, and just acting as a straight exhaust pipe.

[joeb]

we went out at lunch and checked my coworkers 96 skylark. the inlet temp was 380F and the outlet was 500F. he has what appears to be a resonator right behind the cat and it is the same size as the cat and we measured the temp of the resonator and the inlet/outlet seemed to have the same temp. my sons 97 grand prix has a resonator and it is about twice as long as the cat. different shapes too. i know my other car has pre-cats before the main cat so i wonder if the exhaust from the pre-cat should be the same temp as the skylark cat inlet temp? hmm, maybe the skylark has pre-cats. I am not sure. sounds like my main cat is not functioning well. maybe it is plugged too?

[JasonA]

Just wondering...how are you determining the exhaust temperature? With one of those IR temperature pointy-gun-thingys? I would think to get more accurate data, you'd need a pyrometer in the exhaust stream itself.

[joeb]

yes. its a IR gun. if my temp is 100F lower and my friends is 100F higher, I would consider that a good indication of something not working the same. i went to another site and i got a good response as to the percent of gases in the exhaust. i think a 4 gas analyzer will tell me fairly quickly if the converter is working or not. the lite did go off after several days. could be something as simple as air temp. it is cooler here this weekend.

[danbuc]

The cat on your car is shot. All catalytic converters (while working) have a higher outpuit tempertaure than the input. This is because the catalytic converter stores and uses oxygen to combine with unburned hydrocarbons from incomplete combustion, which result in a higher output temperature. This is why a car that is running rich, can cause the cat to get "cherry red". The increase in fuel, when combined with the stored oxygen, produces excessively high temperatures resulting in a damaged cat.

If you've ever used a butane powered soldering iron, they work in a very similar way. A ceramic screen is heated by the butane flame. Once it get hot enough, the flame is extinguished, and the ceramic screen is kept hot via the butane gas. This is the same ast the cat being kept hot, but unburned fuel ingiting within it.