High HC cause??

[Ken Cunningham]

I just passed my bi-annual CA 'Test Only,' but barely. I was right on the HC line at both 15 and 25mph. The tech told me that the cat convertor is prolly on its way out. Do you agree?

I passed two years ago with flying colors. My car is set up identically as far as the cat, smog chip, egr etc. Here are my numbers from 4/3/02:

[mph rpm %CO2 %O2 HCmax HCmeas CO%max CO%meas NOmax NOmeas]

15 1588 14.9 0.3 110 31 0.71 0.05 1025 338
25 1179 14.6 0.6 85 17 0.59 0.03 885 207

Here are my numbers from yesterday (3/6/04):

15 1525 14.8 0.2 110 110 0.71 0.12 772 31
25 1210 14.6 0.5 85 85 0.59 0.17 711 65

I have lots of headroom left on CO% and NO, but am out of room on HC. Also interesting to note that MAX level for NO have come down in the last two years! I hope that trend doesn't continue.

TIA

 

[gofstbuick]

HC is unburned fuel. While it may be true that the cat is on it's way out, you should examine the other gases first. If you were to make the mixture richer and the HC went down and the NOx went up, I would have to say that you were touching on a lean mixture. But, if you made the mixture richer and HC stayed the same, and CO went up and NOx stayed the same, then you may have cause to believe that the cat is on it's way out. This is assuming the all the element of ignition and compression are within spec.