Bad Cat converter

Feb 26, 2008 2 Replies

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Tube Audio 18 years ago

I just had my emissions / smog check here in California for my 1987 Mercedes

300E and the NOx were really high. Very close to failing.

I suspect a bad cat. I measure the temp of the cat with a fluke infrared and measured 245C or 473F. The temperature was the same at the front, middle and back of the cat. The car was running at operating temp, I did this after I came home from work and the water temp was near 100C

Shouldn't the reading be closer to 426C or 800F?

Ideas? It looks like the original cat , the car has 175,000 miles

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Paul 18 years ago

Temp should be closer to 500 with a noticeable inlet to outlet difference.

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Mike 18 years ago

First thing to check would be the EGR system. Make sure the EGR valve is working properly and that none of the passages are plugged or restricted. Other factors that can contribute to high NOx are ignition timing too far advanced and any cooling system problem that causes the engine to run hot.

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